From a0d77192f69d829915c27d19de52ce35ca28ce4b Mon Sep 17 00:00:00 2001 From: Alexander Potapenko Date: Thu, 11 May 2017 11:07:48 +0000 Subject: [PATCH] [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 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302787 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../Instrumentation/MemorySanitizer.cpp | 7 +++++-- .../MemorySanitizer/pr32842.ll | 20 +++++++++++++++++++ 2 files changed, 25 insertions(+), 2 deletions(-) create mode 100644 test/Instrumentation/MemorySanitizer/pr32842.ll diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp index 15333a5317d..ff753c20a94 100644 --- a/lib/Transforms/Instrumentation/MemorySanitizer.cpp +++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp @@ -1576,13 +1576,16 @@ struct MemorySanitizerVisitor : public InstVisitor { 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); diff --git a/test/Instrumentation/MemorySanitizer/pr32842.ll b/test/Instrumentation/MemorySanitizer/pr32842.ll new file mode 100644 index 00000000000..5d74c9a193b --- /dev/null +++ b/test/Instrumentation/MemorySanitizer/pr32842.ll @@ -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 -- 2.50.1