From fe9414d0ccbf0b26d15a99807e9a8e78719361db Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Mon, 6 May 2019 20:34:05 +0000
Subject: [PATCH] [InstCombine] sink FP negation of operands through select

We don't always get this:

Cond ? -X : -Y --> -(Cond ? X : Y)

...even with the legacy IR form of fneg in the case with extra uses,
and we miss matching with the newer 'fneg' instruction because we
are expecting binops through the rest of the path.

Differential Revision: https://reviews.llvm.org/D61604

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@360075 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineSelect.cpp           | 12 ++++++++++++
 test/Transforms/InstCombine/fneg.ll             | 17 ++++++++---------
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index d0292b640fe..5a14726bee2 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -333,6 +333,18 @@ Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
                             TI->getType());
   }
 
+  // Cond ? -X : -Y --> -(Cond ? X : Y)
+  Value *X, *Y;
+  if (match(TI, m_FNeg(m_Value(X))) && match(FI, m_FNeg(m_Value(Y))) &&
+      (TI->hasOneUse() || FI->hasOneUse())) {
+    Value *NewSel = Builder.CreateSelect(Cond, X, Y, SI.getName() + ".v", &SI);
+    // TODO: Remove the hack for the binop form when the unary op is optimized
+    //       properly with all IR passes.
+    if (TI->getOpcode() != Instruction::FNeg)
+      return BinaryOperator::CreateFNegFMF(NewSel, cast<BinaryOperator>(TI));
+    return UnaryOperator::CreateFNeg(NewSel);
+  }
+
   // Only handle binary operators (including two-operand getelementptr) with
   // one-use here. As with the cast case above, it may be possible to relax the
   // one-use constraint, but that needs be examined carefully since it may not
diff --git a/test/Transforms/InstCombine/fneg.ll b/test/Transforms/InstCombine/fneg.ll
index 4a5f033629d..9c4e72f5f06 100644
--- a/test/Transforms/InstCombine/fneg.ll
+++ b/test/Transforms/InstCombine/fneg.ll
@@ -161,9 +161,8 @@ define <4 x double> @fdiv_op0_constant_fneg_vec(<4 x double> %x) {
 
 define <2 x double> @fneg_fneg_sel(<2 x double> %x, <2 x double> %y, i1 %cond) {
 ; CHECK-LABEL: @fneg_fneg_sel(
-; CHECK-NEXT:    [[N1:%.*]] = fneg <2 x double> [[X:%.*]]
-; CHECK-NEXT:    [[N2:%.*]] = fneg <2 x double> [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], <2 x double> [[N1]], <2 x double> [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], <2 x double> [[X:%.*]], <2 x double> [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = fneg <2 x double> [[SEL_V]]
 ; CHECK-NEXT:    ret <2 x double> [[SEL]]
 ;
   %n1 = fneg <2 x double> %x
@@ -178,8 +177,8 @@ define float @fneg_fneg_sel_extra_use1(float %x, float %y, i1 %cond) {
 ; CHECK-LABEL: @fneg_fneg_sel_extra_use1(
 ; CHECK-NEXT:    [[N1:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[N1]])
-; CHECK-NEXT:    [[N2:%.*]] = fneg float [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], float [[N1]], float [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], float [[X]], float [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = fneg float [[SEL_V]]
 ; CHECK-NEXT:    ret float [[SEL]]
 ;
   %n1 = fneg float %x
@@ -191,10 +190,10 @@ define float @fneg_fneg_sel_extra_use1(float %x, float %y, i1 %cond) {
 
 define float @fneg_fneg_sel_extra_use2(float %x, float %y, i1 %cond) {
 ; CHECK-LABEL: @fneg_fneg_sel_extra_use2(
-; CHECK-NEXT:    [[N1:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    [[N2:%.*]] = fneg float [[Y:%.*]]
 ; CHECK-NEXT:    call void @use(float [[N2]])
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], float [[N1]], float [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], float [[X:%.*]], float [[Y]]
+; CHECK-NEXT:    [[SEL:%.*]] = fneg float [[SEL_V]]
 ; CHECK-NEXT:    ret float [[SEL]]
 ;
   %n1 = fneg float %x
@@ -210,8 +209,8 @@ define float @fsub_fsub_sel_extra_use1(float %x, float %y, i1 %cond) {
 ; CHECK-LABEL: @fsub_fsub_sel_extra_use1(
 ; CHECK-NEXT:    [[N1:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[N1]])
-; CHECK-NEXT:    [[N2:%.*]] = fsub float -0.000000e+00, [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], float [[N1]], float [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], float [[X]], float [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = fsub float -0.000000e+00, [[SEL_V]]
 ; CHECK-NEXT:    ret float [[SEL]]
 ;
   %n1 = fsub float -0.0, %x
-- 
2.50.1