[InstCombine] fix fmul reassociation to avoid creating an extra fdiv
This was supposed to be an NFC refactoring that will eventually allow
eliminating the isFast() predicate, but there's a rare possibility
that we would pessimize the code as shown in the test case because
we failed to check 'hasOneUse()' properly. This version also removes
an inefficiency of the old code; we would look for:
(X * C) * C1 --> X * (C * C1)
...but that pattern is always handled by
SimplifyAssociativeOrCommutative().
llvm-svn: 327404
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 47d5d5f..56de5ed 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -557,14 +557,28 @@
// Reassociate constant RHS with another constant to form constant expression.
if (I.isFast() && match(Op1, m_Constant(C)) && C->isFiniteNonZeroFP()) {
+ Constant *C1;
+ if (match(Op0, m_OneUse(m_FDiv(m_Constant(C1), m_Value(X))))) {
+ // (C1 / X) * C --> (C * C1) / X
+ Constant *CC1 = ConstantExpr::getFMul(C, C1);
+ if (CC1->isNormalFP())
+ return BinaryOperator::CreateFDivFMF(CC1, X, &I);
+ }
+ if (match(Op0, m_FDiv(m_Value(X), m_Constant(C1)))) {
+ // (X / C1) * C --> X * (C / C1)
+ Constant *CDivC1 = ConstantExpr::getFDiv(C, C1);
+ if (CDivC1->isNormalFP())
+ return BinaryOperator::CreateFMulFMF(X, CDivC1, &I);
+
+ // If the constant was a denormal, try reassociating differently.
+ // (X / C1) * C --> X / (C1 / C)
+ Constant *C1DivC = ConstantExpr::getFDiv(C1, C);
+ if (Op0->hasOneUse() && C1DivC->isNormalFP())
+ return BinaryOperator::CreateFDivFMF(X, C1DivC, &I);
+ }
+
// Let MDC denote an expression in one of these forms:
// X * C, C/X, X/C, where C is a constant.
- //
- // Try to simplify "MDC * Constant"
- if (isFMulOrFDivWithConstant(Op0))
- if (Value *V = foldFMulConst(cast<Instruction>(Op0), C, &I))
- return replaceInstUsesWith(I, V);
-
// (MDC +/- C1) * C => (MDC * C) +/- (C1 * C)
Instruction *FAddSub = dyn_cast<Instruction>(Op0);
if (FAddSub &&