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[MemCpyOpt] Failure to eliminate memcpy #85560

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DianQK opened this issue Mar 17, 2024 · 0 comments · Fixed by #87190
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[MemCpyOpt] Failure to eliminate memcpy #85560

DianQK opened this issue Mar 17, 2024 · 0 comments · Fixed by #87190
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llvm:transforms missed-optimization

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DianQK commented Mar 17, 2024 •
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I tried the following code:

%0 = type { i8, [753 x i8] }

define void @src(ptr nocapture noundef %arg) local_unnamed_addr {
bb:
  %i = alloca %0, align 1
  call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(754) %i, ptr noundef nonnull align 1 dereferenceable(754) %arg, i64 754, i1 false)
  %i1 = getelementptr inbounds i8, ptr %i, i64 1
  store i8 1, ptr %arg, align 1
  %i2 = getelementptr inbounds i8, ptr %arg, i64 1
  call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(753) %i2, ptr noundef nonnull align 1 dereferenceable(753) %i1, i64 753, i1 false)
  ret void
}

define void @tgt(ptr nocapture noundef %arg) local_unnamed_addr {
bb:
  store i8 1, ptr %arg, align 1
  ret void
}

; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg) #0

attributes #0 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }

We can eliminate all memcpy.

alive2: https://alive2.llvm.org/ce/z/hCPePV
From: rust-lang/rust#122610 (comment).
@DianQK DianQK self-assigned this Mar 17, 2024
@DianQK DianQK changed the title [MemCpyOpt] Failed to eliminate memcpy [MemCpyOpt] Failure to eliminate memcpy Mar 17, 2024
@DianQK DianQK changed the title [MemCpyOpt] Failure to eliminate memcpy [MemCpyOpt?] Failure to eliminate memcpy Mar 17, 2024
@DianQK DianQK changed the title [MemCpyOpt?] Failure to eliminate memcpy [MemCpyOpt] Failure to eliminate memcpy Mar 28, 2024
@DianQK DianQK mentioned this issue Mar 31, 2024
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@DianQK DianQK mentioned this issue Jul 3, 2024
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@DianQK DianQK closed this as completed in fa24213 Jul 12, 2024
aaryanshukla pushed a commit to aaryanshukla/llvm-project that referenced this issue Jul 14, 2024
@DianQK @aaryanshukla
[MemCpyOpt] Forward memcpy based on the actual copy memory locatio…
293ff48 
…n. (llvm#87190)

Fixes llvm#85560.

We can forward `memcpy` as long as the actual memory location being
copied have not been altered.

alive2: https://alive2.llvm.org/ce/z/q9JaHV
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[MemCpyOpt] Forward memcpy based on the actual copy memory location. DianQK/llvm-project
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@EugeneZelenko @DianQK