From 423f19f2dadee9325766008b63c1faf3c644043b Mon Sep 17 00:00:00 2001 From: Owen Anderson Date: Mon, 7 May 2012 20:47:23 +0000 Subject: Teach reassociate to commute FMul's and FAdd's in order to canonicalize the order of their operands across instructions. This allows for greater CSE opportunities. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156323 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/Reassociate.cpp | 32 ++++++++++++++++++++++++++++---- 1 file changed, 28 insertions(+), 4 deletions(-) (limited to 'lib/Transforms') diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp index cc98ba0..010f17a 100644 --- a/lib/Transforms/Scalar/Reassociate.cpp +++ b/lib/Transforms/Scalar/Reassociate.cpp @@ -1212,10 +1212,34 @@ void Reassociate::ReassociateInst(BasicBlock::iterator &BBI) { BI = NI; } - // Reject cases where it is pointless to do this. - if (!isa(BI) || BI->getType()->isFloatingPointTy() || - BI->getType()->isVectorTy()) - return; // Floating point ops are not associative. + // Floating point binary operators are not associative, but we can still + // commute (some) of them, to canonicalize the order of their operands. + // This can potentially expose more CSE opportunities, and makes writing + // other transformations simpler. + if (isa(BI) && + (BI->getType()->isFloatingPointTy() || BI->getType()->isVectorTy())) { + // FAdd and FMul can be commuted. + if (BI->getOpcode() != Instruction::FMul && + BI->getOpcode() != Instruction::FAdd) + return; + + Value *LHS = BI->getOperand(0); + Value *RHS = BI->getOperand(1); + unsigned LHSRank = getRank(LHS); + unsigned RHSRank = getRank(RHS); + + // Sort the operands by rank. + if (RHSRank < LHSRank) { + BI->setOperand(0, RHS); + BI->setOperand(1, LHS); + } + + return; + } + + // Do not reassociate operations that we do not understand. + if (!isa(BI)) + return; // Do not reassociate boolean (i1) expressions. We want to preserve the // original order of evaluation for short-circuited comparisons that -- cgit v1.1