[llvm] r302787 - [msan] Fix PR32842

[Evgenii Stepanov via llvm-commits]

Looks like you broke MemorySanitizer.ICmpRelational test:

http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/1864/steps/64-bit%20check-msan/logs/stdio

On Thu, May 11, 2017 at 4:07 AM, Alexander Potapenko via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: glider
> Date: Thu May 11 06:07:48 2017
> New Revision: 302787
>
> URL: http://llvm.org/viewvc/llvm-project?rev=302787&view=rev
> Log:
> [msan] Fix PR32842
>
> It turned out that MSan was incorrectly calculating the shadow for int comparisons: it was done by truncating the result of (Shadow1 OR Shadow2) to i1, effectively rendering all bits except LSB useless.
> This approach doesn't work e.g. in the case where the values being compared are even (i.e. have the LSB of the shadow equal to zero).
> Instead, if CreateShadowCast() has to cast a bigger int to i1, we replace the truncation with an ICMP to 0.
>
> This patch doesn't affect the code generated for SPEC 2006 binaries, i.e. there's no performance impact.
>
> For the test case reported in PR32842 MSan with the patch generates a slightly more efficient code:
>
>   orq     %rcx, %rax
>   jne     .LBB0_6
> , instead of:
>
>   orl     %ecx, %eax
>   testb   $1, %al
>   jne     .LBB0_6
>
>
>
> Added:
>     llvm/trunk/test/Instrumentation/MemorySanitizer/pr32842.ll
> Modified:
>     llvm/trunk/lib/Transforms/Instrumentation/MemorySanitizer.cpp
>
> Modified: llvm/trunk/lib/Transforms/Instrumentation/MemorySanitizer.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/MemorySanitizer.cpp?rev=302787&r1=302786&r2=302787&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Instrumentation/MemorySanitizer.cpp (original)
> +++ llvm/trunk/lib/Transforms/Instrumentation/MemorySanitizer.cpp Thu May 11 06:07:48 2017
> @@ -1576,13 +1576,16 @@ struct MemorySanitizerVisitor : public I
>    Value *CreateShadowCast(IRBuilder<> &IRB, Value *V, Type *dstTy,
>                            bool Signed = false) {
>      Type *srcTy = V->getType();
> +    size_t srcSizeInBits = VectorOrPrimitiveTypeSizeInBits(srcTy);
> +    size_t dstSizeInBits = VectorOrPrimitiveTypeSizeInBits(dstTy);
> +    if (srcSizeInBits > 1 && dstSizeInBits == 1)
> +      return IRB.CreateICmpNE(V, getCleanShadow(V));
> +
>      if (dstTy->isIntegerTy() && srcTy->isIntegerTy())
>        return IRB.CreateIntCast(V, dstTy, Signed);
>      if (dstTy->isVectorTy() && srcTy->isVectorTy() &&
>          dstTy->getVectorNumElements() == srcTy->getVectorNumElements())
>        return IRB.CreateIntCast(V, dstTy, Signed);
> -    size_t srcSizeInBits = VectorOrPrimitiveTypeSizeInBits(srcTy);
> -    size_t dstSizeInBits = VectorOrPrimitiveTypeSizeInBits(dstTy);
>      Value *V1 = IRB.CreateBitCast(V, Type::getIntNTy(*MS.C, srcSizeInBits));
>      Value *V2 =
>        IRB.CreateIntCast(V1, Type::getIntNTy(*MS.C, dstSizeInBits), Signed);
>
> Added: llvm/trunk/test/Instrumentation/MemorySanitizer/pr32842.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/MemorySanitizer/pr32842.ll?rev=302787&view=auto
> ==============================================================================
> --- llvm/trunk/test/Instrumentation/MemorySanitizer/pr32842.ll (added)
> +++ llvm/trunk/test/Instrumentation/MemorySanitizer/pr32842.ll Thu May 11 06:07:48 2017
> @@ -0,0 +1,20 @@
> +; Regression test for https://bugs.llvm.org/show_bug.cgi?id=32842
> +;
> +; RUN: opt < %s -msan -S | FileCheck %s
> +;target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
> +target triple = "x86_64-unknown-linux-gnu"
> +
> +define zeroext i1 @_Z1fii(i32 %x, i32 %y) sanitize_memory {
> +entry:
> +  %cmp = icmp slt i32 %x, %y
> +  ret i1 %cmp
> +}
> +
> +; CHECK:      [[X:[^ ]+]] = load{{.*}}__msan_param_tls{{.*}}
> +; CHECK:      [[Y:[^ ]+]] = load{{.*}}__msan_param_tls{{.*}}
> +; CHECK:      [[OR:[^ ]+]] = or i32 [[Y]], [[X]]
> +
> +; Make sure the shadow of the (x < y) comparison isn't truncated to i1.
> +; CHECK-NOT:  trunc i32 [[OR]] to i1
> +; CHECK:      [[CMP:[^ ]+]] = icmp ne i32 [[OR]], 0
> +; CHECK:      store i1 [[CMP]],{{.*}}__msan_retval_tls
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits