[clang] [compiler-rt] Ubsan minimum assumed alignment (PR #166755)

[Eli Friedman via llvm-commits]

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@@ -1749,17 +1751,32 @@ llvm::Value *CodeGenFunction::EmitCXXNewExpr(const CXXNewExpr *E) {
       allocator->isReservedGlobalPlacementOperator())
     result = Builder.CreateLaunderInvariantGroup(result);
 
+  // Check the default alignment of the type and why. Users may incorrectly
+  // return misaligned memory from a replaced operator new without knowing
+  // about default alignment.
+  TypeCheckKind checkKind = CodeGenFunction::TCK_ConstructorCall;
+  CharUnits checkAlignment = result.getAlignment();
+  const TargetInfo &TI = getContext().getTargetInfo();
+  unsigned DefaultTargetAlignment = TI.getNewAlign() / TI.getCharWidth();
+  if (SanOpts.has(SanitizerKind::Alignment) &&
+      (DefaultTargetAlignment >
+       CGM.getContext().getTypeAlignInChars(allocType).getQuantity()) &&
+      !result.getAlignment().isOne() &&
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efriedma-quic wrote:

Why do we need to check `!result.getAlignment().isOne()`?

https://github.com/llvm/llvm-project/pull/166755