[llvm] r237858 - [MemCpyOpt] Don't move the memset when optimizing memset+memcpy.

Nick Lewycky nlewycky at google.com
Wed May 20 18:18:42 PDT 2015 

On 20 May 2015 at 16:55, Ahmed Bougacha <ahmed.bougacha at gmail.com> wrote:

> Author: ab
> Date: Wed May 20 18:55:16 2015
> New Revision: 237858
>
> URL: http://llvm.org/viewvc/llvm-project?rev=237858&view=rev
> Log:
> [MemCpyOpt] Don't move the memset when optimizing memset+memcpy.
>
> Fixes PR23599, another miscompile introduced by r235232: when there is
> another dependency on the destination of the created memset (i.e., the
> part of the original destination that the memcpy doesn't depend on)
> between the memcpy and the original memset, we would insert the created
> memset after the memcpy, and thus after the other dependency.
>
> Instead, insert the created memset right after the old one.
>

New crash. Testcase:

$ cat b.c
void test(int a, char *b, int c) {
  memset(b, 0, a);
  memcpy(b, 0, c);
}

$ clang -cc1 -triple x86_64-pc-linux-gnu -x c b.c -emit-obj -O1 -o /dev/null
b.c:2:3: warning: implicitly declaring library function 'memset' with type
'void *(void *, int, unsigned long)'
  memset(b, 0, a);
  ^
b.c:2:3: note: include the header <string.h> or explicitly provide a
declaration for 'memset'
b.c:3:3: warning: implicitly declaring library function 'memcpy' with type
'void *(void *, const void *, unsigned long)'
  memcpy(b, 0, c);
  ^
b.c:3:3: note: include the header <string.h> or explicitly provide a
declaration for 'memcpy'
Instruction does not dominate all uses!
  %6 = sext i32 %c to i64
  %2 = sub nsw i64 %1, %6
Instruction does not dominate all uses!
  %6 = sext i32 %c to i64
  %5 = getelementptr i8, i8* %b, i64 %6
fatal error: error in backend: Broken function found, compilation aborted!


> Modified:
>     llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
>     llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
>
> Modified: llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp?rev=237858&r1=237857&r2=237858&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp Wed May 20
> 18:55:16 2015
> @@ -874,7 +874,7 @@ bool MemCpyOpt::processMemSetMemCpyDepen
>      if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
>        Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
>
> -  IRBuilder<> Builder(MemCpy->getNextNode());
> +  IRBuilder<> Builder(MemSet->getNextNode());
>
>    // If the sizes have different types, zext the smaller one.
>    if (DestSize->getType() != SrcSize->getType()) {
>
> Modified:
> llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll?rev=237858&r1=237857&r2=237858&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
> (original)
> +++ llvm/trunk/test/Transforms/MemCpyOpt/memset-memcpy-redundant-memset.ll
> Wed May 20 18:55:16 2015
> @@ -3,12 +3,12 @@
>  target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
>
>  ; CHECK-LABEL: define void @test
> -; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src,
> i64 %src_size, i32 1, i1 false)
>  ; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i64 %src_size
>  ; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i64 %dst_size, %src_size
>  ; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i64 %dst_size, %src_size
>  ; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i64 0, i64 [[SIZEDIFF]]
>  ; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[DST]], i8 %c, i64
> [[SIZE]], i32 1, i1 false)
> +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src,
> i64 %src_size, i32 1, i1 false)
>  ; CHECK-NEXT: ret void
>  define void @test(i8* %src, i64 %src_size, i8* %dst, i64 %dst_size, i8
> %c) {
>    call void @llvm.memset.p0i8.i64(i8* %dst, i8 %c, i64 %dst_size, i32 1,
> i1 false)
> @@ -17,13 +17,13 @@ define void @test(i8* %src, i64 %src_siz
>  }
>
>  ; CHECK-LABEL: define void @test_different_types_i32_i64
> -; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src,
> i64 %src_size, i32 1, i1 false)
>  ; CHECK-DAG: [[DSTSIZE:%[0-9]+]] = zext i32 %dst_size to i64
>  ; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i64 %src_size
>  ; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i64 [[DSTSIZE]], %src_size
>  ; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i64 [[DSTSIZE]], %src_size
>  ; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i64 0, i64 [[SIZEDIFF]]
>  ; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[DST]], i8 %c, i64
> [[SIZE]], i32 1, i1 false)
> +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src,
> i64 %src_size, i32 1, i1 false)
>  ; CHECK-NEXT: ret void
>  define void @test_different_types_i32_i64(i8* %dst, i8* %src, i32
> %dst_size, i64 %src_size, i8 %c) {
>    call void @llvm.memset.p0i8.i32(i8* %dst, i8 %c, i32 %dst_size, i32 1,
> i1 false)
> @@ -32,13 +32,13 @@ define void @test_different_types_i32_i6
>  }
>
>  ; CHECK-LABEL: define void @test_different_types_i128_i32
> -; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dst, i8* %src,
> i32 %src_size, i32 1, i1 false)
>  ; CHECK-DAG: [[SRCSIZE:%[0-9]+]] = zext i32 %src_size to i128
>  ; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i128
> [[SRCSIZE]]
>  ; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i128 %dst_size, [[SRCSIZE]]
>  ; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i128 %dst_size, [[SRCSIZE]]
>  ; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i128 0, i128
> [[SIZEDIFF]]
>  ; CHECK-NEXT: call void @llvm.memset.p0i8.i128(i8* [[DST]], i8 %c, i128
> [[SIZE]], i32 1, i1 false)
> +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dst, i8* %src,
> i32 %src_size, i32 1, i1 false)
>  ; CHECK-NEXT: ret void
>  define void @test_different_types_i128_i32(i8* %dst, i8* %src, i128
> %dst_size, i32 %src_size, i8 %c) {
>    call void @llvm.memset.p0i8.i128(i8* %dst, i8 %c, i128 %dst_size, i32
> 1, i1 false)
> @@ -47,13 +47,13 @@ define void @test_different_types_i128_i
>  }
>
>  ; CHECK-LABEL: define void @test_different_types_i32_i128
> -; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i128(i8* %dst, i8* %src,
> i128 %src_size, i32 1, i1 false)
>  ; CHECK-DAG: [[DSTSIZE:%[0-9]+]] = zext i32 %dst_size to i128
>  ; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i128 %src_size
>  ; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i128 [[DSTSIZE]], %src_size
>  ; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i128 [[DSTSIZE]], %src_size
>  ; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i128 0, i128
> [[SIZEDIFF]]
>  ; CHECK-NEXT: call void @llvm.memset.p0i8.i128(i8* [[DST]], i8 %c, i128
> [[SIZE]], i32 1, i1 false)
> +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i128(i8* %dst, i8* %src,
> i128 %src_size, i32 1, i1 false)
>  ; CHECK-NEXT: ret void
>  define void @test_different_types_i32_i128(i8* %dst, i8* %src, i32
> %dst_size, i128 %src_size, i8 %c) {
>    call void @llvm.memset.p0i8.i32(i8* %dst, i8 %c, i32 %dst_size, i32 1,
> i1 false)
> @@ -62,13 +62,13 @@ define void @test_different_types_i32_i1
>  }
>
>  ; CHECK-LABEL: define void @test_different_types_i64_i32
> -; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dst, i8* %src,
> i32 %src_size, i32 1, i1 false)
>  ; CHECK-DAG: [[SRCSIZE:%[0-9]+]] = zext i32 %src_size to i64
>  ; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i64 [[SRCSIZE]]
>  ; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i64 %dst_size, [[SRCSIZE]]
>  ; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i64 %dst_size, [[SRCSIZE]]
>  ; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i64 0, i64 [[SIZEDIFF]]
>  ; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[DST]], i8 %c, i64
> [[SIZE]], i32 1, i1 false)
> +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dst, i8* %src,
> i32 %src_size, i32 1, i1 false)
>  ; CHECK-NEXT: ret void
>  define void @test_different_types_i64_i32(i8* %dst, i8* %src, i64
> %dst_size, i32 %src_size, i8 %c) {
>    call void @llvm.memset.p0i8.i64(i8* %dst, i8 %c, i64 %dst_size, i32 1,
> i1 false)
> @@ -102,12 +102,12 @@ define void @test_align_memcpy(i8* %src,
>
>  ; CHECK-LABEL: define void @test_non_i8_dst_type
>  ; CHECK-NEXT: %dst = bitcast i64* %dst_pi64 to i8*
> -; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src,
> i64 %src_size, i32 1, i1 false)
>  ; CHECK-DAG: [[DST:%[0-9]+]] = getelementptr i8, i8* %dst, i64 %src_size
>  ; CHECK-DAG: [[ULE:%[0-9]+]] = icmp ule i64 %dst_size, %src_size
>  ; CHECK-DAG: [[SIZEDIFF:%[0-9]+]] = sub i64 %dst_size, %src_size
>  ; CHECK-DAG: [[SIZE:%[0-9]+]] = select i1 [[ULE]], i64 0, i64 [[SIZEDIFF]]
>  ; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[DST]], i8 %c, i64
> [[SIZE]], i32 1, i1 false)
> +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src,
> i64 %src_size, i32 1, i1 false)
>  ; CHECK-NEXT: ret void
>  define void @test_non_i8_dst_type(i8* %src, i64 %src_size, i64*
> %dst_pi64, i64 %dst_size, i8 %c) {
>    %dst = bitcast i64* %dst_pi64 to i8*
>
>
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