Update PatternMatcher to match both FNeg(X) and FSub(+-0.0, X) in FNeg_match

[spatel]

LGTM - thanks for splitting it off.

llvm/unittests/IR/PatternMatch.cpp

605

Nit: I thought that was a zero on first look rather than an 'O'. Porbably better to spell that out as "One".

[cameron.mcinally]

llvm/unittests/IR/PatternMatch.cpp

605

Sorry, I missed this comment in the Phab email. Will update now...

llvm/include/llvm/IR/PatternMatch.h

 }
 
 template <typename Op_t> struct FNeg_match {
   Op_t X;
 
   FNeg_match(const Op_t &Op) : X(Op) {}
   template <typename OpTy> bool match(OpTy *V) {
     auto *FPMO = dyn_cast<FPMathOperator>(V);
-    if (!FPMO || FPMO->getOpcode() != Instruction::FSub)
-      return false;
+    if (!FPMO) return false;
+
+    if (FPMO->getOpcode() == Instruction::FNeg)
+      return X.match(FPMO->getOperand(0));
+
+    if (FPMO->getOpcode() == Instruction::FSub) {
       if (FPMO->hasNoSignedZeros()) {
         // With 'nsz', any zero goes.
         if (!cstfp_pred_ty<is_any_zero_fp>().match(FPMO->getOperand(0)))
           return false;
       } else {
         // Without 'nsz', we need fsub -0.0, X exactly.
         if (!cstfp_pred_ty<is_neg_zero_fp>().match(FPMO->getOperand(0)))
           return false;
       }
+
       return X.match(FPMO->getOperand(1));
     }
+
+    return false;
+  }
 };
 
 /// Match 'fneg X' as 'fsub -0.0, X'.
 template <typename OpTy>
 inline FNeg_match<OpTy>
 m_FNeg(const OpTy &X) {
   return FNeg_match<OpTy>(X);
 }

llvm/unittests/IR/PatternMatch.cpp

TEST_F(PatternMatchTest, VectorUndefFloat) {
 
   EXPECT_FALSE(match(ScalarUndef, m_AnyZeroFP()));
   EXPECT_FALSE(match(VectorUndef, m_AnyZeroFP()));
   EXPECT_TRUE(match(ScalarZero, m_AnyZeroFP()));
   EXPECT_TRUE(match(VectorZero, m_AnyZeroFP()));
   EXPECT_TRUE(match(VectorZeroUndef, m_AnyZeroFP()));
 }
 
+TEST_F(PatternMatchTest, FloatingPointFNeg) {
+  Type *FltTy = IRB.getFloatTy();
+  Value *O = ConstantFP::get(FltTy, 1.0);
+  Value *Z = ConstantFP::get(FltTy, 0.0);
+  Value *NZ = ConstantFP::get(FltTy, -0.0);
+  Value *V = IRB.CreateFNeg(O);
+  Value *V1 = IRB.CreateFSub(NZ, O);
+  Value *V2 = IRB.CreateFSub(Z, O);
+  Value *V3 = IRB.CreateFAdd(NZ, O);
+  Value *Match;
+
+  // Test FNeg(1.0)
+  EXPECT_TRUE(match(V, m_FNeg(m_Value(Match))));
+  EXPECT_EQ(O, Match);
+
+  // Test FSub(-0.0, 1.0)
+  EXPECT_TRUE(match(V1, m_FNeg(m_Value(Match))));
+  EXPECT_EQ(O, Match);
+
+  // Test FSub(0.0, 1.0)
+  EXPECT_FALSE(match(V2, m_FNeg(m_Value(Match))));
+  cast<Instruction>(V2)->setHasNoSignedZeros(true);
+  EXPECT_TRUE(match(V2, m_FNeg(m_Value(Match))));
+  EXPECT_EQ(O, Match);
+
+  // Test FAdd(-0.0, 1.0)
+  EXPECT_FALSE(match(V3, m_FNeg(m_Value(Match))));
+}
+
 template <typename T> struct MutableConstTest : PatternMatchTest { };
 
 typedef ::testing::Types<std::tuple<Value*, Instruction*>,
                          std::tuple<const Value*, const Instruction *>>
     MutableConstTestTypes;
 TYPED_TEST_CASE(MutableConstTest, MutableConstTestTypes);
 
 TYPED_TEST(MutableConstTest, ICmp) {