From 927aaff33897bb24070863daf19d567840ab10bb Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Mon, 7 Jun 2021 11:48:45 -0400
Subject: [PATCH] [InstCombine] refactor match clauses; NFC

We need to adjust the FMF propagation on at least
one of these transforms as discussed in:
https://llvm.org/PR49654
...so this should make it easier to intersect flags.
---
 .../InstCombine/InstCombineAddSub.cpp         | 21 +++++++++++--------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 2a77f56e569..2e0d3bf0a24 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -2125,27 +2125,30 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
 /// 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) {
+  // This is limited with one-use because fneg is assumed better for
+  // reassociation and cheaper in codegen than fmul/fdiv.
+  // TODO: Should the m_OneUse restriction be removed?
+  Instruction *FNegOp;
+  if (!match(&I, m_FNeg(m_OneUse(m_Instruction(FNegOp)))))
+    return nullptr;
+
   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.
+  // Fold negation into constant operand.
   // -(X * C) --> X * (-C)
-  // FIXME: It's arguable whether these should be m_OneUse or not. The current
-  // belief is that the FNeg allows for better reassociation opportunities.
-  if (match(&I, m_FNeg(m_OneUse(m_FMul(m_Value(X), m_Constant(C))))))
+  if (match(FNegOp, 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))))))
+  if (match(FNegOp, 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))))))
+  if (match(FNegOp, m_FDiv(m_Constant(C), m_Value(X))))
     return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
 
   // With NSZ [ counter-example with -0.0: -(-0.0 + 0.0) != 0.0 + -0.0 ]:
   // -(X + C) --> -X + -C --> -C - X
-  if (I.hasNoSignedZeros() &&
-      match(&I, m_FNeg(m_OneUse(m_FAdd(m_Value(X), m_Constant(C))))))
+  if (I.hasNoSignedZeros() && match(FNegOp, m_FAdd(m_Value(X), m_Constant(C))))
     return BinaryOperator::CreateFSubFMF(ConstantExpr::getFNeg(C), X, &I);
 
   return nullptr;