[ubsan] Skip alignment checks which are folded away
Don't emit alignment checks which the IR constant folder throws away.
I've tested this out on X86FastISel.cpp. While this doesn't decrease
end-to-end compile-time significantly, it results in 122 fewer type
checks (1% reduction) overall, without adding any real complexity.
Differential Revision: https://reviews.llvm.org/D37544
llvm-svn: 314752
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index e87c4a9..cd2e8e1 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -618,6 +618,7 @@
auto PtrToAlloca =
dyn_cast<llvm::AllocaInst>(Ptr->stripPointerCastsNoFollowAliases());
+ llvm::Value *True = llvm::ConstantInt::getTrue(getLLVMContext());
llvm::Value *IsNonNull = nullptr;
bool IsGuaranteedNonNull =
SkippedChecks.has(SanitizerKind::Null) || PtrToAlloca;
@@ -629,8 +630,7 @@
// The IR builder can constant-fold the null check if the pointer points to
// a constant.
- IsGuaranteedNonNull =
- IsNonNull == llvm::ConstantInt::getTrue(getLLVMContext());
+ IsGuaranteedNonNull = IsNonNull == True;
// Skip the null check if the pointer is known to be non-null.
if (!IsGuaranteedNonNull) {
@@ -684,7 +684,8 @@
PtrAsInt, llvm::ConstantInt::get(IntPtrTy, AlignVal - 1));
llvm::Value *Aligned =
Builder.CreateICmpEQ(Align, llvm::ConstantInt::get(IntPtrTy, 0));
- Checks.push_back(std::make_pair(Aligned, SanitizerKind::Alignment));
+ if (Aligned != True)
+ Checks.push_back(std::make_pair(Aligned, SanitizerKind::Alignment));
}
}