From 83252dcfe61aaebcb6bc117e71dc12968729513f Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Tue, 20 Jul 2010 21:07:09 +0000 Subject: Follow the implementation approach suggested by PR6687, which generates more efficient and more obviously conformant code. We now test for overflow of the multiply then force the result to -1 if so. On X86, this generates nice code like this: __Z4testl: ## @_Z4testl ## BB#0: ## %entry subl $12, %esp movl $4, %eax mull 16(%esp) testl %edx, %edx movl $-1, %ecx cmovel %eax, %ecx movl %ecx, (%esp) call __Znam addl $12, %esp ret git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@108927 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/CGExprCXX.cpp | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) (limited to 'lib/CodeGen/CGExprCXX.cpp') diff --git a/lib/CodeGen/CGExprCXX.cpp b/lib/CodeGen/CGExprCXX.cpp index cc34b3d75c..d3e7919224 100644 --- a/lib/CodeGen/CGExprCXX.cpp +++ b/lib/CodeGen/CGExprCXX.cpp @@ -440,7 +440,7 @@ static llvm::Value *EmitCXXNewAllocSize(ASTContext &Context, // new double[n] // where n is 2^30 on a 32-bit machine or 2^62 on a 64-bit machine. Because // of this, we need to detect the overflow and ensure that an exception is - // called by invoking std::__throw_length_error. + // called by forcing the size to -1 on overflow. llvm::Value *UMulF = CGF.CGM.getIntrinsic(llvm::Intrinsic::umul_with_overflow, &SizeTy, 1); llvm::Value *MulRes = CGF.Builder.CreateCall2(UMulF, NumElements, @@ -448,15 +448,26 @@ static llvm::Value *EmitCXXNewAllocSize(ASTContext &Context, TypeSize.getQuantity())); // Branch on the overflow bit to the overflow block, which is lazily created. llvm::Value *DidOverflow = CGF.Builder.CreateExtractValue(MulRes, 1); + // Get the normal result of the multiplication. + llvm::Value *V = CGF.Builder.CreateExtractValue(MulRes, 0); llvm::BasicBlock *NormalBB = CGF.createBasicBlock("no_overflow"); + llvm::BasicBlock *OverflowBB = CGF.createBasicBlock("overflow"); - CGF.Builder.CreateCondBr(DidOverflow, CGF.getThrowLengthErrorBB(), NormalBB); + CGF.Builder.CreateCondBr(DidOverflow, OverflowBB, NormalBB); + + llvm::BasicBlock *PrevBB = CGF.Builder.GetInsertBlock(); + + // We just need the overflow block to build a PHI node. + CGF.EmitBlock(OverflowBB); CGF.EmitBlock(NormalBB); - // Get the normal result of the multiplication. - llvm::Value *V = CGF.Builder.CreateExtractValue(MulRes, 0); - + llvm::PHINode *PN = CGF.Builder.CreatePHI(V->getType()); + + PN->addIncoming(V, PrevBB); + PN->addIncoming(llvm::Constant::getAllOnesValue(V->getType()), OverflowBB); + V = PN; + // And add the cookie padding if necessary. if (!CookiePadding.isZero()) V = CGF.Builder.CreateAdd(V, -- cgit v1.2.3-70-g09d2