Skip to content

Add str::is_char_boundary ASCII successor optimization hint - #161570

Open
briantkelley wants to merge 1 commit into
rust-lang:mainfrom
briantkelley:str-split-at-ascii-boundary
Open

Add str::is_char_boundary ASCII successor optimization hint#161570
briantkelley wants to merge 1 commit into
rust-lang:mainfrom
briantkelley:str-split-at-ascii-boundary

Conversation

@briantkelley

@briantkelley briantkelley commented Aug 23, 2026

Copy link
Copy Markdown

Indexing and splitting &str after an ASCII character is a common pattern in parsing or tokenizing a string.

Today, if the index or split occurs after the ASCII character (e.g., a line feed or a double quote), the operation incurs a runtime character boundary check, which adversely affects runtime performance and increases binary size.

This commit enables the optimizer to eliminate that runtime check by adding a hint about a continuation byte's predecessor.

@briantkelley
Add str::is_char_boundary ASCII successor optimization hint
c58263e 
Indexing and splitting `&str` after an ASCII character is a common
pattern in parsing or tokenizing a string.

Today, if the index or split occurs *after* the ASCII character (e.g.,
a line feed or a double quote), the operation incurs a runtime character
boundary check, which adversely affects runtime performance and
increases binary size.

This commit enables the optimizer to eliminate that runtime check by
adding a hint about a continuation byte's predecessor.
@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 23, 2026
@rustbot

rustbot commented Aug 23, 2026

Copy link
Copy Markdown
Collaborator

Thanks for the pull request, and welcome! The Rust Project has assigned @dingxiangfei2009 (or someone else) to review your changes, you should hear from them (or someone else) within the next two weeks.

Please see the contribution instructions and our LLM policy for more information.

Why was this reviewer chosen?

The reviewer was selected based on:

  • Owners of files modified in this PR: compiler
  • compiler expanded to 75 candidates
  • Random selection from 19 candidates

@rust-log-analyzer

rust-log-analyzer commented Aug 23, 2026

Copy link
Copy Markdown
Collaborator

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot) 

---- [codegen] tests/codegen-llvm/str-range-indexing.rs stdout ----
------FileCheck stdout------------------------------

------FileCheck stderr------------------------------
/checkout/tests/codegen-llvm/str-range-indexing.rs:50:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:216:2: note: found here
 %9 = icmp sgt i8 %self.i18.i, -65
 ^~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:59:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:250:2: note: found here
 %extract.t.i = icmp slt i8 %_15.i, 0
 ^~~~~~~~~~~~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:64:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:287:2: note: found here
 %extract.t.i = icmp slt i8 %_15.i, 0
 ^~~~~~~~~~~~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:78:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:357:2: note: found here
 %1 = icmp sgt i8 %self.i18.i, -65
 ^~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:87:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:396:2: note: found here
 %extract.t.i = icmp slt i8 %_15.i, 0
 ^~~~~~~~~~~~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:92:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:431:2: note: found here
 %extract.t.i = icmp slt i8 %_15.i, 0
 ^~~~~~~~~~~~~~~~~~~

Input file: /checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll
Check file: /checkout/tests/codegen-llvm/str-range-indexing.rs

-dump-input=help explains the following input dump.

Input was:
<<<<<<
        .
        .
        .
      116:  %2 = load i8, ptr %1, align 8, !range !14, !noundef !7 
      117:  %_20 = trunc nuw i8 %2 to i1 
      118:  %3 = load i64, ptr %range, align 8, !noundef !7 
      119:  %_7.0 = add nuw i64 %_19, 1 
      120:  %spec.select = select i1 %_20, i64 %_7.0, i64 %3 
      121:  %_6.i = icmp ugt i64 %spec.select, %_7.0 
      122:  br i1 %_6.i, label %bb3, label %bb3.i 
      123:  
      124: bb3.i: ; preds = %bb2 
      125:  %_9.i = icmp eq i64 %spec.select, %slice.1 
      126:  br i1 %_9.i, label %bb8, label %bb5.i 
      127:  
      128: bb5.i: ; preds = %bb3.i 
      129:  %4 = icmp eq i64 %spec.select, 0 
      130:  br i1 %4, label %bb8.i, label %bb18.i 
      131:  
      132: bb8.i: ; preds = %bb18.i, %bb5.i 
      133:  %_14.i = icmp eq i64 %_7.0, %slice.1 
      134:  br i1 %_14.i, label %bb8, label %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit 
      135:  
      136: bb18.i: ; preds = %bb5.i 
      137:  %self.i = getelementptr inbounds nuw i8, ptr %slice.0, i64 %spec.select 
      138:  %self1.i = load i8, ptr %self.i, align 1, !alias.scope !15, !noundef !7 
      139:  %_10.i = icmp sgt i8 %self1.i, -65 
      140:  br i1 %_10.i, label %bb8.i, label %bb3 
      141:  
      142: _RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit: ; preds = %bb8.i 
      143:  %self2.i = getelementptr inbounds nuw i8, ptr %slice.0, i64 %_7.0 
      144:  %self3.i = load i8, ptr %self2.i, align 1, !alias.scope !15, !noundef !7 
      145:  %5 = icmp sgt i8 %self3.i, -65 
      146:  br i1 %5, label %bb8, label %bb3 
      147:  
      148: bb8: ; preds = %bb8.i, %bb3.i, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit 
      149:  %_13 = sub nuw i64 %_7.0, %spec.select 
      150:  %_15 = getelementptr inbounds nuw i8, ptr %slice.0, i64 %spec.select 
      151:  br label %bb3 
      152:  
      153: bb3: ; preds = %bb18.i, %bb2, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit, %start, %bb8 
      154:  %_0.sroa.4.0 = phi i64 [ %_13, %bb8 ], [ undef, %start ], [ undef, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit ], [ undef, %bb2 ], [ undef, %bb18.i ] 
      155:  %_0.sroa.0.0 = phi ptr [ %_15, %bb8 ], [ null, %start ], [ null, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit ], [ null, %bb2 ], [ null, %bb18.i ] 
      156:  %6 = insertvalue { ptr, i64 } poison, ptr %_0.sroa.0.0, 0 
      157:  %7 = insertvalue { ptr, i64 } %6, i64 %_0.sroa.4.0, 1 
      158:  ret { ptr, i64 } %7 
      159: } 
      160:  
      161: ; Function Attrs: uwtable 
      162: define { ptr, i64 } @index_range_inclusive(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, ptr dead_on_return noalias nofree noundef readonly align 8 captures(none) dereferenceable(24) %range) unnamed_addr #1 { 
      163: start: 
      164:  tail call void @llvm.experimental.noalias.scope.decl(metadata !18) 
      165:  tail call void @llvm.experimental.noalias.scope.decl(metadata !21) 
      166:  %0 = load i64, ptr %range, align 8, !alias.scope !18, !noalias !23, !noundef !7 
      167:  %1 = getelementptr inbounds nuw i8, ptr %range, i64 16 
      168:  %2 = load i64, ptr %1, align 8, !alias.scope !18, !noalias !23, !noundef !7 
      169:  %_7.i = icmp ult i64 %2, %slice.1 
      170:  br i1 %_7.i, label %bb1.i, label %bb16.i, !prof !25 
      171:  
      172: bb1.i: ; preds = %start 
      173:  %3 = getelementptr inbounds nuw i8, ptr %range, i64 8 
      174:  %4 = load i8, ptr %3, align 8, !range !14, !alias.scope !18, !noalias !23, !noundef !7 
      175:  %exhausted.i = trunc nuw i8 %4 to i1 
      176:  %_9.0.i = add nuw i64 %2, 1 
      177:  %spec.select.i = select i1 %exhausted.i, i64 %_9.0.i, i64 %0 
      178:  %_10.not.i = icmp ugt i64 %spec.select.i, %_9.0.i 
      179:  br i1 %_10.not.i, label %bb16.i, label %bb6.i, !prof !26 
      180:  
      181: bb16.sink.split.i: ; preds = %bb5.i17.i, %bb5.i.i 
      182:  %.sink.i = phi i64 [ -1, %bb5.i.i ], [ %2, %bb5.i17.i ] 
      183:  %slice.0.sink.i = phi ptr [ %6, %bb5.i.i ], [ %slice.0, %bb5.i17.i ] 
      184:  %self2.i20.i = getelementptr i8, ptr %slice.0.sink.i, i64 %.sink.i 
      185:  %_15.i21.i = load i8, ptr %self2.i20.i, align 1, !alias.scope !21, !noalias !27, !noundef !7 
      186:  %extract.t.i22.i = icmp slt i8 %_15.i21.i, 0 
      187:  tail call void @llvm.assume(i1 %extract.t.i22.i) 
      188:  br label %bb16.i 
      189:  
      190: bb16.i: ; preds = %bb16.sink.split.i, %bb1.i, %start 
      191:  %end.sroa.0.0.i = phi i64 [ %_9.0.i, %bb1.i ], [ %2, %start ], [ %_9.0.i, %bb16.sink.split.i ] 
      192:  %start1.sroa.0.0.i = phi i64 [ %spec.select.i, %bb1.i ], [ %0, %start ], [ %spec.select.i, %bb16.sink.split.i ] 
      193: ; call core::str::slice_error_fail 
      194:  tail call void @_RNvNtCsfPQd7m5fVAo_4core3str16slice_error_fail(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %start1.sroa.0.0.i, i64 noundef %end.sroa.0.0.i, ptr noalias nofree noundef nonnull readonly align 8 captures(address, read_provenance) dereferenceable(24) @alloc_78ba39ad615490512fcb426d9931de2f) #6, !noalias !18 
      195:  unreachable 
      196:  
      197: bb6.i: ; preds = %bb1.i 
      198:  %5 = icmp ne i64 %spec.select.i, 0 
      199:  %_3.not.i.i = icmp ult i64 %spec.select.i, %slice.1 
      200:  %or.cond.i = and i1 %5, %_3.not.i.i 
      201:  br i1 %or.cond.i, label %bb5.i.i, label %bb2.i13.i 
      202:  
      203: bb5.i.i: ; preds = %bb6.i 
      204:  %6 = getelementptr i8, ptr %slice.0, i64 %spec.select.i 
      205:  %self.i.i = load i8, ptr %6, align 1, !alias.scope !28, !noalias !27, !noundef !7 
      206:  %7 = icmp sgt i8 %self.i.i, -65 
      207:  br i1 %7, label %bb2.i13.i, label %bb16.sink.split.i 
      208:  
      209: bb2.i13.i: ; preds = %bb5.i.i, %bb6.i 
      210:  %_3.not.i14.i = icmp ult i64 %_9.0.i, %slice.1 
      211:  br i1 %_3.not.i14.i, label %bb5.i17.i, label %_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index.exit 
      212:  
      213: bb5.i17.i: ; preds = %bb2.i13.i 
      214:  %8 = getelementptr i8, ptr %slice.0, i64 %_9.0.i 
      215:  %self.i18.i = load i8, ptr %8, align 1, !alias.scope !31, !noalias !27, !noundef !7 
      216:  %9 = icmp sgt i8 %self.i18.i, -65 
not:50      !~~~~~~~~                          error: no match expected
      217:  br i1 %9, label %_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index.exit, label %bb16.sink.split.i 
      218:  
      219: _RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index.exit: ; preds = %bb2.i13.i, %bb5.i17.i 
      220:  %new_len.i = sub nuw i64 %_9.0.i, %spec.select.i 
      221:  %self2.i = getelementptr inbounds nuw i8, ptr %slice.0, i64 %spec.select.i 
      222:  %10 = insertvalue { ptr, i64 } poison, ptr %self2.i, 0 
      223:  %11 = insertvalue { ptr, i64 } %10, i64 %new_len.i, 1 
      224:  ret { ptr, i64 } %11 
      225: } 
      226:  
      227: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read, inaccessiblemem: write) uwtable 
      228: define { ptr, i64 } @get_range_to(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range) unnamed_addr #2 { 
      229: start: 
      230:  %0 = icmp eq i64 %range, 0 
      231:  br i1 %0, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread, label %bb2.i 
      232:  
      233: bb2.i: ; preds = %start 
      234:  %_3.not.i = icmp ult i64 %range, %slice.1 
      235:  br i1 %_3.not.i, label %bb5.i, label %bb3.i 
      236:  
      237: bb3.i: ; preds = %bb2.i 
      238:  %1 = icmp eq i64 %range, %slice.1 
      239:  br i1 %1, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread, label %4 
      240:  
      241: bb5.i: ; preds = %bb2.i 
      242:  %2 = getelementptr i8, ptr %slice.0, i64 %range 
      243:  %self.i = load i8, ptr %2, align 1, !alias.scope !34, !noundef !7 
      244:  %3 = icmp sgt i8 %self.i, -65 
      245:  br i1 %3, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit 
      246:  
      247: _RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit: ; preds = %bb5.i 
      248:  %self2.i = getelementptr i8, ptr %2, i64 -1 
      249:  %_15.i = load i8, ptr %self2.i, align 1, !alias.scope !34, !noundef !7 
      250:  %extract.t.i = icmp slt i8 %_15.i, 0 
not:59      !~~~~~~~~~~~~~~~~~~                   error: no match expected
      251:  tail call void @llvm.assume(i1 %extract.t.i) 
      252:  br label %4 
      253:  
      254: _RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread: ; preds = %bb5.i, %start, %bb3.i 
      255:  br label %4 
      256:  
      257: 4: ; preds = %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit, %bb3.i, %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread 
      258:  %5 = phi ptr [ %slice.0, %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread ], [ null, %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit ], [ null, %bb3.i ] 
      259:  %6 = insertvalue { ptr, i64 } poison, ptr %5, 0 
      260:  %7 = insertvalue { ptr, i64 } %6, i64 %range, 1 
      261:  ret { ptr, i64 } %7 
      262: } 
      263:  
      264: ; Function Attrs: uwtable 
      265: define { ptr, i64 } @index_range_to(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range) unnamed_addr #1 { 
      266: start: 
      267:  %0 = icmp eq i64 %range, 0 
      268:  br i1 %0, label %bb2, label %bb2.i 
      269:  
      270: bb2.i: ; preds = %start 
      271:  %_3.not.i = icmp ult i64 %range, %slice.1 
      272:  br i1 %_3.not.i, label %bb5.i, label %bb3.i 
      273:  
      274: bb3.i: ; preds = %bb2.i 
      275:  %1 = icmp eq i64 %range, %slice.1 
      276:  br i1 %1, label %bb2, label %bb3, !prof !37 
      277:  
      278: bb5.i: ; preds = %bb2.i 
      279:  %2 = getelementptr i8, ptr %slice.0, i64 %range 
      280:  %self.i = load i8, ptr %2, align 1, !alias.scope !38, !noundef !7 
      281:  %3 = icmp sgt i8 %self.i, -65 
      282:  br i1 %3, label %bb2, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit 
      283:  
      284: _RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit: ; preds = %bb5.i 
      285:  %self2.i = getelementptr i8, ptr %2, i64 -1 
      286:  %_15.i = load i8, ptr %self2.i, align 1, !alias.scope !38, !noundef !7 
      287:  %extract.t.i = icmp slt i8 %_15.i, 0 
not:64      !~~~~~~~~~~~~~~~~~~                   error: no match expected
      288:  tail call void @llvm.assume(i1 %extract.t.i) 
      289:  br label %bb3 
      290:  
      291: bb3: ; preds = %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit, %bb3.i 
      292: ; call core::str::slice_error_fail 
      293:  tail call void @_RNvNtCsfPQd7m5fVAo_4core3str16slice_error_fail(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef 0, i64 noundef %range, ptr noalias nofree noundef readonly align 8 captures(address, read_provenance) dereferenceable(24) @alloc_841057aa1436332b84cea2376bbac6e2) #6 
      294:  unreachable 
      295:  
      296: bb2: ; preds = %bb5.i, %start, %bb3.i 
      297:  %4 = insertvalue { ptr, i64 } poison, ptr %slice.0, 0 
      298:  %5 = insertvalue { ptr, i64 } %4, i64 %range, 1 
      299:  ret { ptr, i64 } %5 
      300: } 
      301:  
      302: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read) uwtable 
      303: define { ptr, i64 } @get_range_to_inclusive(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range) unnamed_addr #0 { 
      304: start: 
      305:  %_3.not = icmp ult i64 %range, %slice.1 
      306:  br i1 %_3.not, label %bb2, label %bb3 
      307:  
      308: bb2: ; preds = %start 
      309:  %_7.0 = add nuw i64 %range, 1 
      310:  %_14.i = icmp eq i64 %_7.0, %slice.1 
      311:  br i1 %_14.i, label %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit.thread, label %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit 
      312:  
      313: _RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit: ; preds = %bb2 
      314:  %self2.i = getelementptr inbounds nuw i8, ptr %slice.0, i64 %_7.0 
      315:  %self3.i = load i8, ptr %self2.i, align 1, !alias.scope !41, !noundef !7 
      316:  %0 = icmp sgt i8 %self3.i, -65 
      317:  br i1 %0, label %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit.thread, label %bb3 
      318:  
      319: _RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit.thread: ; preds = %bb2, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit 
      320:  br label %bb3 
      321:  
      322: bb3: ; preds = %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit.thread, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit, %start 
      323:  %_0.sroa.4.0 = phi i64 [ undef, %start ], [ %_7.0, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit ], [ %_7.0, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit.thread ] 
      324:  %_0.sroa.0.0 = phi ptr [ null, %start ], [ null, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit ], [ %slice.0, %_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range.exit.thread ] 
      325:  %1 = insertvalue { ptr, i64 } poison, ptr %_0.sroa.0.0, 0 
      326:  %2 = insertvalue { ptr, i64 } %1, i64 %_0.sroa.4.0, 1 
      327:  ret { ptr, i64 } %2 
      328: } 
      329:  
      330: ; Function Attrs: uwtable 
      331: define { ptr, i64 } @index_range_to_inclusive(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range) unnamed_addr #1 { 
      332: start: 
      333:  %_7.i = icmp ult i64 %range, %slice.1 
      334:  br i1 %_7.i, label %bb2.i13.i, label %bb16.i, !prof !25 
      335:  
      336: bb16.sink.split.i: ; preds = %bb5.i17.i 
      337:  %self2.i20.i = getelementptr i8, ptr %slice.0, i64 %range 
      338:  %_15.i21.i = load i8, ptr %self2.i20.i, align 1, !alias.scope !44, !noalias !47, !noundef !7 
      339:  %extract.t.i22.i = icmp slt i8 %_15.i21.i, 0 
      340:  tail call void @llvm.assume(i1 %extract.t.i22.i) 
      341:  br label %bb16.i 
      342:  
      343: bb16.i: ; preds = %bb16.sink.split.i, %start 
      344:  %end.sroa.0.0.i = phi i64 [ %range, %start ], [ %_9.0.i, %bb16.sink.split.i ] 
      345: ; call core::str::slice_error_fail 
      346:  tail call void @_RNvNtCsfPQd7m5fVAo_4core3str16slice_error_fail(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef 0, i64 noundef %end.sroa.0.0.i, ptr noalias nofree noundef nonnull readonly align 8 captures(address, read_provenance) dereferenceable(24) @alloc_3332297e63c267e94af75aa1c181a976) #6, !noalias !50 
      347:  unreachable 
      348:  
      349: bb2.i13.i: ; preds = %start 
      350:  %_9.0.i = add nuw i64 %range, 1 
      351:  %_3.not.i14.i = icmp ult i64 %_9.0.i, %slice.1 
      352:  br i1 %_3.not.i14.i, label %bb5.i17.i, label %_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index.exit 
      353:  
      354: bb5.i17.i: ; preds = %bb2.i13.i 
      355:  %0 = getelementptr i8, ptr %slice.0, i64 %_9.0.i 
      356:  %self.i18.i = load i8, ptr %0, align 1, !alias.scope !51, !noalias !47, !noundef !7 
      357:  %1 = icmp sgt i8 %self.i18.i, -65 
not:78      !~~~~~~~~                          error: no match expected
      358:  br i1 %1, label %_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index.exit, label %bb16.sink.split.i 
      359:  
      360: _RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index.exit: ; preds = %bb2.i13.i, %bb5.i17.i 
      361:  %2 = insertvalue { ptr, i64 } poison, ptr %slice.0, 0 
      362:  %3 = insertvalue { ptr, i64 } %2, i64 %_9.0.i, 1 
      363:  ret { ptr, i64 } %3 
      364: } 
      365:  
      366: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read, inaccessiblemem: write) uwtable 
      367: define { ptr, i64 } @get_range_from(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range) unnamed_addr #2 { 
      368: start: 
      369:  %0 = icmp eq i64 %range, 0 
      370:  br i1 %0, label %.thread, label %bb2.i 
      371:  
      372: bb2.i: ; preds = %start 
      373:  %_3.not.i = icmp ult i64 %range, %slice.1 
      374:  br i1 %_3.not.i, label %bb5.i, label %bb3.i 
      375:  
      376: bb3.i: ; preds = %bb2.i 
      377:  %1 = icmp eq i64 %range, %slice.1 
      378:  %_89 = sub nuw i64 %slice.1, %range 
      379:  %_1010 = getelementptr inbounds nuw i8, ptr %slice.0, i64 %range 
      380:  %spec.select = select i1 %1, ptr %_1010, ptr null 
      381:  br label %.thread 
      382:  
      383: bb5.i: ; preds = %bb2.i 
      384:  %2 = getelementptr i8, ptr %slice.0, i64 %range 
      385:  %self.i = load i8, ptr %2, align 1, !alias.scope !54, !noundef !7 
      386:  %3 = icmp sgt i8 %self.i, -65 
      387:  br i1 %3, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread11, label %.thread18 
      388:  
      389: _RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread11: ; preds = %bb5.i 
      390:  %_813 = sub nuw i64 %slice.1, %range 
      391:  br label %.thread 
      392:  
      393: .thread18: ; preds = %bb5.i 
      394:  %self2.i = getelementptr i8, ptr %2, i64 -1 
      395:  %_15.i = load i8, ptr %self2.i, align 1, !alias.scope !54, !noundef !7 
      396:  %extract.t.i = icmp slt i8 %_15.i, 0 
not:87      !~~~~~~~~~~~~~~~~~~                   error: no match expected
      397:  tail call void @llvm.assume(i1 %extract.t.i) 
      398:  br label %.thread 
      399:  
      400: .thread: ; preds = %start, %bb3.i, %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread11, %.thread18 
      401:  %4 = phi i64 [ undef, %.thread18 ], [ %_813, %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread11 ], [ %_89, %bb3.i ], [ %slice.1, %start ] 
      402:  %5 = phi ptr [ null, %.thread18 ], [ %2, %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit.thread11 ], [ %spec.select, %bb3.i ], [ %slice.0, %start ] 
      403:  %6 = insertvalue { ptr, i64 } poison, ptr %5, 0 
      404:  %7 = insertvalue { ptr, i64 } %6, i64 %4, 1 
      405:  ret { ptr, i64 } %7 
      406: } 
      407:  
      408: ; Function Attrs: uwtable 
      409: define { ptr, i64 } @index_range_from(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range) unnamed_addr #1 { 
      410: start: 
      411:  %0 = icmp eq i64 %range, 0 
      412:  br i1 %0, label %bb2, label %bb2.i 
      413:  
      414: bb2.i: ; preds = %start 
      415:  %_3.not.i = icmp ult i64 %range, %slice.1 
      416:  br i1 %_3.not.i, label %bb5.i, label %bb3.i 
      417:  
      418: bb3.i: ; preds = %bb2.i 
      419:  %1 = icmp eq i64 %range, %slice.1 
      420:  br i1 %1, label %bb2, label %bb3, !prof !37 
      421:  
      422: bb5.i: ; preds = %bb2.i 
      423:  %2 = getelementptr i8, ptr %slice.0, i64 %range 
      424:  %self.i = load i8, ptr %2, align 1, !alias.scope !57, !noundef !7 
      425:  %3 = icmp sgt i8 %self.i, -65 
      426:  br i1 %3, label %bb2, label %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit 
      427:  
      428: _RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit: ; preds = %bb5.i 
      429:  %self2.i = getelementptr i8, ptr %2, i64 -1 
      430:  %_15.i = load i8, ptr %self2.i, align 1, !alias.scope !57, !noundef !7 
      431:  %extract.t.i = icmp slt i8 %_15.i, 0 
not:92      !~~~~~~~~~~~~~~~~~~                   error: no match expected
      432:  tail call void @llvm.assume(i1 %extract.t.i) 
      433:  br label %bb3 
      434:  
      435: bb3: ; preds = %_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary.exit, %bb3.i 
      436: ; call core::str::slice_error_fail 
      437:  tail call void @_RNvNtCsfPQd7m5fVAo_4core3str16slice_error_fail(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance) %slice.0, i64 noundef %slice.1, i64 noundef %range, i64 noundef %slice.1, ptr noalias nofree noundef readonly align 8 captures(address, read_provenance) dereferenceable(24) @alloc_ccfa578a8c08566fbe0712e308271001) #6 
      438:  unreachable 
      439:  
      440: bb2: ; preds = %bb5.i, %start, %bb3.i 
      441:  %_12 = sub nuw i64 %slice.1, %range 
      442:  %_14 = getelementptr inbounds nuw i8, ptr %slice.0, i64 %range 
      443:  %4 = insertvalue { ptr, i64 } poison, ptr %_14, 0 
      444:  %5 = insertvalue { ptr, i64 } %4, i64 %_12, 1 
      445:  ret { ptr, i64 } %5 
      446: } 
      447:  
      448: ; Function Attrs: mustprogress nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) 
      449: declare void @llvm.assume(i1 noundef) #3 
      450:  
      451: ; core::str::slice_error_fail 
      452: ; Function Attrs: cold noinline noreturn uwtable 
      453: declare void @_RNvNtCsfPQd7m5fVAo_4core3str16slice_error_fail(ptr noalias nofree noundef nonnull readonly captures(address, read_provenance), i64 noundef, i64 noundef, i64 noundef, ptr noalias nofree noundef readonly align 8 captures(address, read_provenance) dereferenceable(24)) unnamed_addr #4 
      454:  
      455: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) 
      456: declare void @llvm.experimental.noalias.scope.decl(metadata) #5 
      457:  
      458: attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read) uwtable "frame-pointer"="non-leaf" "probe-stack"="inline-asm" "target-cpu"="generic" "target-features"="+v8a,+outline-atomics" } 
      459: attributes #1 = { uwtable "frame-pointer"="non-leaf" "probe-stack"="inline-asm" "target-cpu"="generic" "target-features"="+v8a,+outline-atomics" } 
      460: attributes #2 = { mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: read, inaccessiblemem: write) uwtable "frame-pointer"="non-leaf" "probe-stack"="inline-asm" "target-cpu"="generic" "target-features"="+v8a,+outline-atomics" } 
      461: attributes #3 = { mustprogress nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) } 
      462: attributes #4 = { cold noinline noreturn uwtable "frame-pointer"="non-leaf" "probe-stack"="inline-asm" "target-cpu"="generic" "target-features"="+v8a,+outline-atomics" } 
      463: attributes #5 = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) } 
      464: attributes #6 = { noinline noreturn } 
      465:  
      466: !llvm.module.flags = !{!0, !1, !2} 
      467: !llvm.ident = !{!3} 
      468:  
      469: !0 = !{i32 8, !"PIC Level", i32 2} 
      470: !1 = !{i32 7, !"uwtable", i32 2} 
      471: !2 = !{i32 7, !"frame-pointer", i32 1} 
      472: !3 = !{!"rustc version 1.100.0-nightly (1a5080cfc 2026-08-22)"} 
      473: !4 = !{!5} 
      474: !5 = distinct !{!5, !6, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range: %slice.0"} 
      475: !6 = distinct !{!6, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range"} 
      476: !7 = !{} 
      477: !8 = !{!"branch_weights", i32 1073205, i32 2146410443} 
      478: !9 = !{!10} 
      479: !10 = distinct !{!10, !11, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range: %slice.0"} 
      480: !11 = distinct !{!11, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range"} 
      481: !12 = !{!"branch_weights", i32 2146410443, i32 1073205} 
      482: !13 = !{!"branch_weights", !"expected", i32 -2147483648, i32 0} 
      483: !14 = !{i8 0, i8 2} 
      484: !15 = !{!16} 
      485: !16 = distinct !{!16, !17, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range: %slice.0"} 
      486: !17 = distinct !{!17, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range"} 
      487: !18 = !{!19} 
      488: !19 = distinct !{!19, !20, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index: %self"} 
      489: !20 = distinct !{!20, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index"} 
      490: !21 = !{!22} 
      491: !22 = distinct !{!22, !20, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index: %slice.0"} 
      492: !23 = !{!22, !24} 
      493: !24 = distinct !{!24, !20, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index: argument 2"} 
      494: !25 = !{!"branch_weights", !"expected", i32 2000, i32 1} 
      495: !26 = !{!"branch_weights", !"expected", i32 1, i32 2000} 
      496: !27 = !{!19, !24} 
      497: !28 = !{!29, !22} 
      498: !29 = distinct !{!29, !30, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      499: !30 = distinct !{!30, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
      500: !31 = !{!32, !22} 
      501: !32 = distinct !{!32, !33, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      502: !33 = distinct !{!33, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
      503: !34 = !{!35} 
      504: !35 = distinct !{!35, !36, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      505: !36 = distinct !{!36, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
      506: !37 = !{!"branch_weights", !"expected", i32 2145766520, i32 1717128} 
      507: !38 = !{!39} 
      508: !39 = distinct !{!39, !40, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      509: !40 = distinct !{!40, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
      510: !41 = !{!42} 
      511: !42 = distinct !{!42, !43, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range: %slice.0"} 
      512: !43 = distinct !{!43, !"_RNvNtNtCsfPQd7m5fVAo_4core3str6traits11check_range"} 
      513: !44 = !{!45} 
      514: !45 = distinct !{!45, !46, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index: %slice.0"} 
      515: !46 = distinct !{!46, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index"} 
      516: !47 = !{!48, !49} 
      517: !48 = distinct !{!48, !46, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index: %self"} 
      518: !49 = distinct !{!49, !46, !"_RNvXsb_NtNtCsfPQd7m5fVAo_4core3str6traitsINtNtNtB9_3ops5range14RangeInclusivejEINtNtNtB9_5slice5index10SliceIndexeE5index: argument 2"} 
      519: !50 = !{!48} 
      520: !51 = !{!52, !45} 
      521: !52 = distinct !{!52, !53, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      522: !53 = distinct !{!53, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
      523: !54 = !{!55} 
      524: !55 = distinct !{!55, !56, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      525: !56 = distinct !{!56, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
      526: !57 = !{!58} 
      527: !58 = distinct !{!58, !59, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary: %self.0"} 
      528: !59 = distinct !{!59, !"_RNvMNtCsfPQd7m5fVAo_4core3stre16is_char_boundary"} 
>>>>>>

------------------------------------------

error: verification with 'FileCheck' failed
status: exit status: 1
command: "/usr/lib/llvm-21/bin/FileCheck" "--input-file" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll" "/checkout/tests/codegen-llvm/str-range-indexing.rs" "--check-prefix=CHECK" "--allow-unused-prefixes" "--dump-input-context" "100"
stdout: none
--- stderr -------------------------------
/checkout/tests/codegen-llvm/str-range-indexing.rs:50:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:216:2: note: found here
 %9 = icmp sgt i8 %self.i18.i, -65
 ^~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:59:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:250:2: note: found here
 %extract.t.i = icmp slt i8 %_15.i, 0
 ^~~~~~~~~~~~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:64:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp
              ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen-llvm/str-range-indexing/str-range-indexing.ll:287:2: note: found here
 %extract.t.i = icmp slt i8 %_15.i, 0
 ^~~~~~~~~~~~~~~~~~~
/checkout/tests/codegen-llvm/str-range-indexing.rs:78:15: error: CHECK-NOT: excluded string found in input
// CHECK-NOT: %{{.+}} = icmp

@fmease

fmease commented Aug 23, 2026

Copy link
Copy Markdown
Member

r? libs

@rustbot rustbot assigned nia-e and unassigned dingxiangfei2009 Aug 23, 2026
@nia-e

nia-e commented Aug 23, 2026

Copy link
Copy Markdown
Member

@bors try @rust-timer queue

@rust-timer

This comment has been minimized.

Sign in to view
@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 23, 2026
@rust-bors

This comment has been minimized.

Sign in to view
rust-bors Bot pushed a commit that referenced this pull request Aug 23, 2026
@bors
Auto merge of #161570 - briantkelley:str-split-at-ascii-boundary, r=<…
95df97f 
…try>

Add `str::is_char_boundary` ASCII successor optimization hint
@rust-bors

rust-bors Bot commented Aug 23, 2026

Copy link
Copy Markdown
Contributor

☀️ Try build successful (CI)
Build commit: 95df97f (95df97fde3309c5b7f4ff2641e86dd7845185438)
Base parent: 9a4ad59 (9a4ad59ae3073b013cd62f53f8349ddc61a012e8)

@rust-timer

This comment has been minimized.

Sign in to view
@rust-timer

rust-timer commented Aug 23, 2026

Copy link
Copy Markdown
Collaborator

Finished benchmarking commit (95df97f): comparison URL.

Overall result: ❌ regressions - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

mean range count
Regressions ❌
(primary)		 0.7% [0.5%, 1.1%] 3
Regressions ❌
(secondary)		 3.0% [0.1%, 7.0%] 16
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 0.7% [0.5%, 1.1%] 3

Max RSS (memory usage)

Results (primary -4.2%, secondary 2.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 - - 0
Regressions ❌
(secondary)		 4.2% [2.7%, 5.8%] 2
Improvements ✅
(primary)		 -4.2% [-5.0%, -3.1%] 3
Improvements ✅
(secondary)		 -2.2% [-2.2%, -2.2%] 1
All ❌✅ (primary) -4.2% [-5.0%, -3.1%] 3

Cycles

Results (secondary 4.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 - - 0
Regressions ❌
(secondary)		 4.3% [1.1%, 7.7%] 9
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) - - 0

Binary size

Results (primary 0.2%, secondary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 0.2% [0.0%, 0.5%] 8
Regressions ❌
(secondary)		 0.4% [0.3%, 0.4%] 12
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 0.2% [0.0%, 0.5%] 8

Bootstrap: 468.884s -> 469.334s (0.10%)
Artifact size: 400.29 MiB -> 400.31 MiB (0.01%)

@rustbot rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Aug 23, 2026
@nia-e

nia-e commented Aug 23, 2026

Copy link
Copy Markdown
Member

these are strong enough results to register as meaningful I think. usually we avoid assert_uncheckeds for this reason ^^ this is also one area of code where it's unfortunately going up be hard to beat the optimiser i fear, but feel free to try.

@rustbot author

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 23, 2026
@rustbot

rustbot commented Aug 23, 2026

Copy link
Copy Markdown
Collaborator

Reminder, once the PR becomes ready for a review, use @rustbot ready.

@briantkelley

briantkelley commented Aug 24, 2026

Copy link
Copy Markdown
Author

Alright, thanks for the feedback. Looks like there are two main follow ups:

  1. Look into mitigating the regressions, primarily around debug. I think the opt regressions are due to more inlining, but I'll need to get clear evidence for that.
  2. Figure out a workaround for the LLVM 21 regression since the optimization relies on a pass only available in LLVM 22.

This branch has not been deployed

No deployments
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

No reviews

Assignees

@nia-e nia-e

Labels

perf-regression Performance regression. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue.

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

7 participants

@briantkelley @rustbot @rust-log-analyzer @fmease @nia-e @rust-timer @dingxiangfei2009