Re-apply "[ubsan] Sanity-check shift amounts before truncation"
This re-applies r293343 (reverts commit r293475) with a fix for an
assertion failure caused by a missing integer cast. I tested this patch
by using the built compiler to compile X86FastISel.cpp.o with ubsan.
Original commit message:
Ubsan does not report UB shifts in some cases where the shift exponent
needs to be truncated to match the type of the shift base. We perform a
range check on the truncated shift amount, leading to false negatives.
Fix the issue (PR27271) by performing the range check on the original
shift amount.
Differential Revision: https://reviews.llvm.org/D29234
llvm-svn: 293572
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 1b85c45..12b14be 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2751,8 +2751,8 @@
isa<llvm::IntegerType>(Ops.LHS->getType())) {
CodeGenFunction::SanitizerScope SanScope(&CGF);
SmallVector<std::pair<Value *, SanitizerMask>, 2> Checks;
- llvm::Value *WidthMinusOne = GetWidthMinusOneValue(Ops.LHS, RHS);
- llvm::Value *ValidExponent = Builder.CreateICmpULE(RHS, WidthMinusOne);
+ llvm::Value *WidthMinusOne = GetWidthMinusOneValue(Ops.LHS, Ops.RHS);
+ llvm::Value *ValidExponent = Builder.CreateICmpULE(Ops.RHS, WidthMinusOne);
if (SanitizeExponent) {
Checks.push_back(
@@ -2767,12 +2767,14 @@
llvm::BasicBlock *Cont = CGF.createBasicBlock("cont");
llvm::BasicBlock *CheckShiftBase = CGF.createBasicBlock("check");
Builder.CreateCondBr(ValidExponent, CheckShiftBase, Cont);
+ llvm::Value *PromotedWidthMinusOne =
+ (RHS == Ops.RHS) ? WidthMinusOne
+ : GetWidthMinusOneValue(Ops.LHS, RHS);
CGF.EmitBlock(CheckShiftBase);
- llvm::Value *BitsShiftedOff =
- Builder.CreateLShr(Ops.LHS,
- Builder.CreateSub(WidthMinusOne, RHS, "shl.zeros",
- /*NUW*/true, /*NSW*/true),
- "shl.check");
+ llvm::Value *BitsShiftedOff = Builder.CreateLShr(
+ Ops.LHS, Builder.CreateSub(PromotedWidthMinusOne, RHS, "shl.zeros",
+ /*NUW*/ true, /*NSW*/ true),
+ "shl.check");
if (CGF.getLangOpts().CPlusPlus) {
// In C99, we are not permitted to shift a 1 bit into the sign bit.
// Under C++11's rules, shifting a 1 bit into the sign bit is