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
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 @@
BI = NI;
}
- // Reject cases where it is pointless to do this.
- if (!isa<BinaryOperator>(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<BinaryOperator>(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<BinaryOperator>(BI))
+ return;
// Do not reassociate boolean (i1) expressions. We want to preserve the
// original order of evaluation for short-circuited comparisons that