Add test for issue 106269

[clubby789]

Closes #106269

Made this an assembly test as the LLVM codegen is still quite verbose and doesn't really indicate the behaviour we want

[rustbot]

r? @Mark-Simulacrum

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[Mark-Simulacrum]

r? @nikic since #106269 (comment) sounded to me like there might be a better way to test here (e.g., detecting the memcmp somehow?)

[clubby789]

The IR looks like this - it's only during codegen that it can be turned into a single comparison

define noundef zeroext i1 @eq1(ptr noalias nocapture noundef readonly align 1 dereferenceable(4) %s1, ptr noalias nocapture noundef readonly align 1 dereferenceable(4) %s2) unnamed_addr {
start:
  %_4 = load i8, ptr %s1, align 1
  %_5 = load i8, ptr %s2, align 1
  %_3 = icmp eq i8 %_4, %_5
  br i1 %_3, label %bb1, label %bb8

bb1:
  %0 = getelementptr inbounds i8, ptr %s1, i64 1
  %_7 = load i8, ptr %0, align 1
  %1 = getelementptr inbounds i8, ptr %s2, i64 1
  %_8 = load i8, ptr %1, align 1
  %_6 = icmp eq i8 %_7, %_8
  br i1 %_6, label %bb2, label %bb8

bb2:
  %2 = getelementptr inbounds i8, ptr %s1, i64 2
  %_10 = load i8, ptr %2, align 1
  %3 = getelementptr inbounds i8, ptr %s2, i64 2
  %_11 = load i8, ptr %3, align 1
  %_9 = icmp eq i8 %_10, %_11
  br i1 %_9, label %bb3, label %bb8

bb3:
  %4 = getelementptr inbounds i8, ptr %s1, i64 3
  %_12 = load i8, ptr %4, align 1
  %5 = getelementptr inbounds i8, ptr %s2, i64 3
  %_13 = load i8, ptr %5, align 1
  %6 = icmp eq i8 %_12, %_13
  br label %bb8

bb8:
  %_0.sroa.0.0 = phi i1 [ %6, %bb3 ], [ false, %bb2 ], [ false, %bb1 ], [ false, %start ]
  ret i1 %_0.sroa.0.0
}

[nikic]

@bors r+ rollup=iffy

Assembly tests are the best we can do for this right now. After llvm/llvm-project#77370 we'd be able to use IR tests for these.

[bors]

📌 Commit 11b0e9a has been approved by nikic

It is now in the queue for this repository.

[bors]

⌛ Testing commit 11b0e9a with merge c016833...

[bors]

💔 Test failed - checks-actions

[clubby789]

Looks like there's always a

        push    rbp
        mov     rbp, rsp
        ....
        pop     rbp

for code on Darwin

@bors r=nikic

[bors]

📌 Commit 7032c92 has been approved by nikic

It is now in the queue for this repository.