From 9ca9daad2175cd57776e7de7fb6f78eb96fc7445 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Wed, 12 Aug 2009 16:37:02 +0000 Subject: Transform -X/C to X/-C, implementing a README.txt entry. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78812 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/InstructionCombining.cpp | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'lib/Transforms') diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 669ef2d516..b875420e5b 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -3077,6 +3077,14 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) { RHS->getValue().exactLogBase2()); return BinaryOperator::CreateAShr(Op0, ShAmt, I.getName()); } + + // -X/C --> X/-C provided the negation doesn't overflow. + if (SubOperator *Sub = dyn_cast(Op0)) + if (isa(Sub->getOperand(0)) && + cast(Sub->getOperand(0))->isNullValue() && + Sub->hasNoSignedOverflow()) + return BinaryOperator::CreateSDiv(Sub->getOperand(1), + ConstantExpr::getNeg(RHS)); } // If the sign bits of both operands are zero (i.e. we can prove they are -- cgit v1.2.3-70-g09d2