[InstCombine] remove flop from lerp patterns
(Y * (1.0 - Z)) + (X * Z) -->
Y - (Y * Z) + (X * Z) -->
Y + Z * (X - Y)
This is part of solving:
https://bugs.llvm.org/show_bug.cgi?id=42716
Factoring eliminates an instruction, so that should be a good canonicalization.
The potential conversion to FMA would be handled by the backend based on target
capabilities.
Differential Revision: https://reviews.llvm.org/D65305
llvm-svn: 367101
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index ba15b02..891370e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1308,6 +1308,22 @@
return Changed ? &I : nullptr;
}
+/// Eliminate an op from a linear interpolation (lerp) pattern.
+static Instruction *factorizeLerp(BinaryOperator &I,
+ InstCombiner::BuilderTy &Builder) {
+ Value *X, *Y, *Z;
+ if (!match(&I, m_c_FAdd(m_OneUse(m_c_FMul(m_Value(Y),
+ m_OneUse(m_FSub(m_FPOne(),
+ m_Value(Z))))),
+ m_OneUse(m_c_FMul(m_Value(X), m_Deferred(Z))))))
+ return nullptr;
+
+ // (Y * (1.0 - Z)) + (X * Z) --> Y + Z * (X - Y) [8 commuted variants]
+ Value *XY = Builder.CreateFSubFMF(X, Y, &I);
+ Value *MulZ = Builder.CreateFMulFMF(Z, XY, &I);
+ return BinaryOperator::CreateFAddFMF(Y, MulZ, &I);
+}
+
/// Factor a common operand out of fadd/fsub of fmul/fdiv.
static Instruction *factorizeFAddFSub(BinaryOperator &I,
InstCombiner::BuilderTy &Builder) {
@@ -1315,6 +1331,10 @@
I.getOpcode() == Instruction::FSub) && "Expecting fadd/fsub");
assert(I.hasAllowReassoc() && I.hasNoSignedZeros() &&
"FP factorization requires FMF");
+
+ if (Instruction *Lerp = factorizeLerp(I, Builder))
+ return Lerp;
+
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
Value *X, *Y, *Z;
bool IsFMul;