From 379d9c1dc6c019eacf851ba1acfaefe8e5f2a587 Mon Sep 17 00:00:00 2001 From: Vedant Kumar Date: Mon, 17 Apr 2017 22:26:07 +0000 Subject: [ubsan] Skip null checks on pointers to the start of an alloca Pointers to the start of an alloca are non-null, so we don't need to emit runtime null checks for them. Testing: check-clang, check-ubsan. This significantly reduces the amount of null checks we emit when compiling X86ISelLowering.cpp. Here are the numbers from patched / unpatched clangs based on r300371. ------------------------------------- | Setup | # of null checks | ------------------------------------- | unpatched, -O0 | 45439 | | patched, -O0 | 25251 | (-44.4%) ------------------------------------- llvm-svn: 300508 --- clang/lib/CodeGen/CGExpr.cpp | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'clang/lib/CodeGen') diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp index 265ef27a46b..b5d6c659e9e 100644 --- a/clang/lib/CodeGen/CGExpr.cpp +++ b/clang/lib/CodeGen/CGExpr.cpp @@ -533,6 +533,15 @@ bool CodeGenFunction::sanitizePerformTypeCheck() const { SanOpts.has(SanitizerKind::Vptr); } +/// Check if a runtime null check for \p Ptr can be omitted. +static bool canOmitPointerNullCheck(llvm::Value *Ptr) { + // Note: do not perform any constant-folding in this function. That is best + // left to the IR builder. + + // Pointers to alloca'd memory are non-null. + return isa(Ptr->stripPointerCastsNoFollowAliases()); +} + void CodeGenFunction::EmitTypeCheck(TypeCheckKind TCK, SourceLocation Loc, llvm::Value *Ptr, QualType Ty, CharUnits Alignment, @@ -554,7 +563,8 @@ void CodeGenFunction::EmitTypeCheck(TypeCheckKind TCK, SourceLocation Loc, bool AllowNullPointers = TCK == TCK_DowncastPointer || TCK == TCK_Upcast || TCK == TCK_UpcastToVirtualBase; if ((SanOpts.has(SanitizerKind::Null) || AllowNullPointers) && - !SkippedChecks.has(SanitizerKind::Null)) { + !SkippedChecks.has(SanitizerKind::Null) && + !canOmitPointerNullCheck(Ptr)) { // The glvalue must not be an empty glvalue. llvm::Value *IsNonNull = Builder.CreateIsNotNull(Ptr); -- cgit v1.2.3