[InstCombine] Add visitFNeg(...) visitor for unary Fneg
Also, break out a helper function, namely foldFNegIntoConstant(...), which performs transforms common between visitFNeg(...) and visitFSub(...).
Differential Revision: https://reviews.llvm.org/D61693
llvm-svn: 361188
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 5f5a94e..421d49f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1821,15 +1821,38 @@
return Changed ? &I : nullptr;
}
+/// This eliminates floating-point negation in either 'fneg(X)' or
+/// 'fsub(-0.0, X)' form by combining into a constant operand.
+static Instruction *foldFNegIntoConstant(Instruction &I) {
+ Value *X;
+ Constant *C;
+
+ // Fold negation into constant operand. This is limited with one-use because
+ // fneg is assumed better for analysis and cheaper in codegen than fmul/fdiv.
+ // -(X * C) --> X * (-C)
+ if (match(&I, m_FNeg(m_OneUse(m_FMul(m_Value(X), m_Constant(C))))))
+ return BinaryOperator::CreateFMulFMF(X, ConstantExpr::getFNeg(C), &I);
+ // -(X / C) --> X / (-C)
+ if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Value(X), m_Constant(C))))))
+ return BinaryOperator::CreateFDivFMF(X, ConstantExpr::getFNeg(C), &I);
+ // -(C / X) --> (-C) / X
+ if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Constant(C), m_Value(X))))))
+ return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
+
+ return nullptr;
+}
+
Instruction *InstCombiner::visitFNeg(UnaryOperator &I) {
if (Value *V = SimplifyFNegInst(I.getOperand(0), I.getFastMathFlags(),
SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
+ if (Instruction *X = foldFNegIntoConstant(I))
+ return X;
+
return nullptr;
}
-
Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
if (Value *V = SimplifyFSubInst(I.getOperand(0), I.getOperand(1),
I.getFastMathFlags(),
@@ -1845,21 +1868,12 @@
if (I.hasNoSignedZeros() && match(Op0, m_PosZeroFP()))
return BinaryOperator::CreateFNegFMF(Op1, &I);
+ if (Instruction *X = foldFNegIntoConstant(I))
+ return X;
+
Value *X, *Y;
Constant *C;
- // Fold negation into constant operand. This is limited with one-use because
- // fneg is assumed better for analysis and cheaper in codegen than fmul/fdiv.
- // -(X * C) --> X * (-C)
- if (match(&I, m_FNeg(m_OneUse(m_FMul(m_Value(X), m_Constant(C))))))
- return BinaryOperator::CreateFMulFMF(X, ConstantExpr::getFNeg(C), &I);
- // -(X / C) --> X / (-C)
- if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Value(X), m_Constant(C))))))
- return BinaryOperator::CreateFDivFMF(X, ConstantExpr::getFNeg(C), &I);
- // -(C / X) --> (-C) / X
- if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Constant(C), m_Value(X))))))
- return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
-
// If Op0 is not -0.0 or we can ignore -0.0: Z - (X - Y) --> Z + (Y - X)
// Canonicalize to fadd to make analysis easier.
// This can also help codegen because fadd is commutative.