From b2d978682b2ddd957d802d209a338f89031fabc0 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Tue, 20 Feb 2018 16:52:17 +0000
Subject: [PATCH] [InstCombine] remove compound fdiv pattern folds

These are fdiv-with-constant-divisor, so they already become
reciprocal multiplies. The last gap for vector ops should be
closed with rL325590.

It's possible that we're missing folds for some edge cases
with denormal intermediate constants after deleting these,
but there are no tests for those patterns, and it would be
better to handle denormals more consistently (and less
conservatively) as noted in TODO comments.

llvm-svn: 325595
---
 .../InstCombine/InstCombineMulDivRem.cpp           | 28 +---------------------
 1 file changed, 1 insertion(+), 27 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 7b15076..17f8e30 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1359,39 +1359,13 @@ Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
       if (Instruction *R = FoldOpIntoSelect(I, SI))
         return R;
 
-  bool AllowReassociate = I.isFast();
   if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
     if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
       if (Instruction *R = FoldOpIntoSelect(I, SI))
         return R;
-
-    if (AllowReassociate) {
-      Constant *C1 = nullptr;
-      Constant *C2 = Op1C;
-      Value *X;
-      Instruction *Res = nullptr;
-
-      if (match(Op0, m_FMul(m_Value(X), m_Constant(C1)))) {
-        // (X*C1)/C2 => X * (C1/C2)
-        Constant *C = ConstantExpr::getFDiv(C1, C2);
-        if (C->isNormalFP())
-          Res = BinaryOperator::CreateFMul(X, C);
-      } else if (match(Op0, m_FDiv(m_Value(X), m_Constant(C1)))) {
-        // (X/C1)/C2 => X /(C2*C1)
-        Constant *C = ConstantExpr::getFMul(C1, C2);
-        if (C->isNormalFP())
-          Res = BinaryOperator::CreateFDiv(X, C);
-      }
-
-      if (Res) {
-        Res->setFastMathFlags(I.getFastMathFlags());
-        return Res;
-      }
-    }
-    return nullptr;
   }
 
-  if (AllowReassociate) {
+  if (I.isFast()) {
     Value *X, *Y;
     if (match(Op0, m_OneUse(m_FDiv(m_Value(X), m_Value(Y)))) &&
         (!isa<Constant>(Y) || !isa<Constant>(Op1))) {
-- 
2.7.4