[msan] Add struct support to CreateShadowCast

[thurstond]

This fixes a TODO in CreateShadowCast, which could be useful for applying handleIntrinsicByApplyingToShadow to intrinsics that return a struct type. Note that getShadowTy already supports structs.

Additionally, this adds assertions to make it easier to know when CreateShadowCast is being used with unsupported types.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

@llvm/pr-subscribers-llvm-transforms

Author: Thurston Dang (thurstond)

Changes

This fixes a TODO in CreateShadowCast, which could be useful for applying handleIntrinsicByApplyingToShadow to intrinsics that return a struct type. Note that getShadowTy already supports structs, hence struct support in CreateShadowCast is the last missing piece.

Additionally, this adds assertions to make it easier to know when CreateShadowCast is being used with unsupported types.

---

Full diff: https://github.com/llvm/llvm-project/pull/130440.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp (+29-1)

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index ba925275faba6..54e34bf9a0b85 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -2562,6 +2562,15 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   Value *CreateShadowCast(IRBuilder<> &IRB, Value *V, Type *dstTy,
                           bool Signed = false) {
     Type *srcTy = V->getType();
+
+    // Shadow types should never be floating-point.
+    assert(!srcTy->isFPOrFPVectorTy());
+    assert(!dstTy->isFPOrFPVectorTy());
+
+    // TODO (though never needed in practice)
+    assert(!srcTy->isArrayTy());
+    assert(!dstTy->isArrayTy());
+
     if (srcTy == dstTy)
       return V;
     size_t srcSizeInBits = VectorOrPrimitiveTypeSizeInBits(srcTy);
@@ -2571,15 +2580,34 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
 
     if (dstTy->isIntegerTy() && srcTy->isIntegerTy())
       return IRB.CreateIntCast(V, dstTy, Signed);
+
     if (dstTy->isVectorTy() && srcTy->isVectorTy() &&
         cast<VectorType>(dstTy)->getElementCount() ==
             cast<VectorType>(srcTy)->getElementCount())
+      // We rely on the assertion at the start of the function that neither
+      // type is a floating-point vector.
       return IRB.CreateIntCast(V, dstTy, Signed);
+
+    if (dstTy->isStructTy() && srcTy->isStructTy() &&
+        cast<StructType>(dstTy)->getNumElements() ==
+            cast<StructType>(srcTy)->getNumElements()) {
+      Value *DStruct = llvm::UndefValue::get(dstTy);
+
+      for (unsigned i = 0, n = cast<StructType>(dstTy)->getNumElements(); i < n;
+           i++) {
+        Value *Elem = IRB.CreateExtractValue(V, i);
+        Type *ElemDstTy = cast<StructType>(dstTy)->getElementType(i);
+        Value *ElemDst = CreateShadowCast(IRB, Elem, ElemDstTy, Signed);
+        DStruct = IRB.CreateInsertValue(DStruct, ElemDst, i);
+      }
+
+      return DStruct;
+    }
+
     Value *V1 = IRB.CreateBitCast(V, Type::getIntNTy(*MS.C, srcSizeInBits));
     Value *V2 =
         IRB.CreateIntCast(V1, Type::getIntNTy(*MS.C, dstSizeInBits), Signed);
     return IRB.CreateBitCast(V2, dstTy);
-    // TODO: handle struct types.
   }
 
   /// Cast an application value to the type of its own shadow.

[github-actions]

✅ With the latest revision this PR passed the undef deprecator.

[vitalybuka]

Do you have example PR where it's used?