From 403717156bc185f545cd343ad3524ded927fc394 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Thu, 9 May 2002 01:29:19 +0000 Subject: [PATCH] Add ability to transform (x - (y - z)) into (x + (z - y)) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2566 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/InstructionCombining.cpp | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index a77bcb95864..9625398017a 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -180,6 +180,19 @@ Instruction *InstCombiner::visitSub(BinaryOperator *I) { if (Value *V = dyn_castNegInst(Op1)) return BinaryOperator::create(Instruction::Add, Op0, V); + // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression is + // not used by anyone else... + // + if (BinaryOperator *Op1I = dyn_cast(Op1)) + if (Op1I->use_size() == 1) { + // Swap the two operands of the subexpr... + Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1); + Op1I->setOperand(0, IIOp1); + Op1I->setOperand(1, IIOp0); + + // Create the new top level add instruction... + return BinaryOperator::create(Instruction::Add, Op0, Op1); + } return 0; }