[ubsan] Emit single check for left shift.

Avoids warning twice on same shift.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176056 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 4 deletions

diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index d76cad2c56..3ec4040a64 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -2407,13 +2407,17 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
   if (CGF.SanOpts->Shift && !CGF.getLangOpts().OpenCL &&
       isa<llvm::IntegerType>(Ops.LHS->getType())) {
     llvm::Value *WidthMinusOne = GetWidthMinusOneValue(Ops.LHS, RHS);
-    // FIXME: Emit the branching explicitly rather than emitting the check
-    // twice.
-    EmitBinOpCheck(Builder.CreateICmpULE(RHS, WidthMinusOne), Ops);
+    llvm::Value *Valid = Builder.CreateICmpULE(RHS, WidthMinusOne);
 
     if (Ops.Ty->hasSignedIntegerRepresentation()) {
+      llvm::BasicBlock *Orig = Builder.GetInsertBlock();
+      llvm::BasicBlock *Cont = CGF.createBasicBlock("cont");
+      llvm::BasicBlock *CheckBitsShifted = CGF.createBasicBlock("check");
+      Builder.CreateCondBr(Valid, CheckBitsShifted, Cont);
+
       // Check whether we are shifting any non-zero bits off the top of the
       // integer.
+      CGF.EmitBlock(CheckBitsShifted);
       llvm::Value *BitsShiftedOff =
         Builder.CreateLShr(Ops.LHS,
                            Builder.CreateSub(WidthMinusOne, RHS, "shl.zeros",
@@ -2428,8 +2432,15 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
         BitsShiftedOff = Builder.CreateLShr(BitsShiftedOff, One);
       }
       llvm::Value *Zero = llvm::ConstantInt::get(BitsShiftedOff->getType(), 0);
-      EmitBinOpCheck(Builder.CreateICmpEQ(BitsShiftedOff, Zero), Ops);
+      llvm::Value *SecondCheck = Builder.CreateICmpEQ(BitsShiftedOff, Zero);
+      CGF.EmitBlock(Cont);
+      llvm::PHINode *P = Builder.CreatePHI(Valid->getType(), 2);
+      P->addIncoming(Valid, Orig);
+      P->addIncoming(SecondCheck, CheckBitsShifted);
+      Valid = P;
     }
+
+    EmitBinOpCheck(Valid, Ops);
   }
   // OpenCL 6.3j: shift values are effectively % word size of LHS.
   if (CGF.getLangOpts().OpenCL)