[llvm] [msan] Convert vector shadow to scalar before zext (PR #96722)

[Thurston Dang via llvm-commits]

https://github.com/thurstond created https://github.com/llvm/llvm-project/pull/96722

    zext does not allow converting vector shadow to scalar, so we must
    manually convert it prior to calling zext in materializeOneCheck,
    for which the 'convertedShadow' parameter isn't actually guaranteed
    to be scalar.

    In contrast, the storeOrigin function already converts the (potentially vector) shadow to scalar; we add a comment to note that it is load bearing.

>From 9a69de62a79717c525985942f30bffedcb86d61d Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Wed, 26 Jun 2024 02:48:02 +0000
Subject: [PATCH]     [msan] Convert vector shadow to scalar before zext

    zext does not allow converting vector shadow to scalar, so we must
    manually convert it prior to calling zext in materializeOneCheck,
    for which the 'convertedShadow' parameter isn't actually guaranteed
    to be scalar.

    In contrast, the storeOrigin function already converts the (potentially vector) shadow to scalar; we add a comment to note that it is load bearing.
---
 llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index f11c1c5933327..442db32025337 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -1283,6 +1283,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     const DataLayout &DL = F.getParent()->getDataLayout();
     const Align OriginAlignment = std::max(kMinOriginAlignment, Alignment);
     TypeSize StoreSize = DL.getTypeStoreSize(Shadow->getType());
+    // ZExt cannot convert between vector and scalar
     Value *ConvertedShadow = convertShadowToScalar(Shadow, IRB);
     if (auto *ConstantShadow = dyn_cast<Constant>(ConvertedShadow)) {
       if (!ClCheckConstantShadow || ConstantShadow->isZeroValue()) {
@@ -1398,6 +1399,8 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     if (instrumentWithCalls(ConvertedShadow) &&
         SizeIndex < kNumberOfAccessSizes && !MS.CompileKernel) {
       FunctionCallee Fn = MS.MaybeWarningFn[SizeIndex];
+      // ZExt cannot convert between vector and scalar
+      ConvertedShadow = convertShadowToScalar(ConvertedShadow, IRB);
       Value *ConvertedShadow2 =
           IRB.CreateZExt(ConvertedShadow, IRB.getIntNTy(8 * (1 << SizeIndex)));
       CallBase *CB = IRB.CreateCall(