GlobalISel: Use the original flags when lowering fneg to fsub

This was ignoring the flag on fneg, and using the source instruction's
flags. Also fixes tests missing from r358702.

Note the expansion itself isn't correct without nnan, but that should
be fixed separately.

llvm-svn: 363637

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
index 67b897fb6a3..09082b20bc9 100644
--- a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
@@ -729,4 +729,50 @@ TEST_F(GISelMITest, FewerElementsPhi) {
 
   EXPECT_TRUE(CheckMachineFunction(*MF, CheckStr)) << *MF;
 }
+
+// FNEG expansion in terms of FSUB
+TEST_F(GISelMITest, LowerFNEG) {
+  if (!TM)
+    return;
+
+  // Declare your legalization info
+  DefineLegalizerInfo(A, {
+    getActionDefinitionsBuilder(G_FSUB).legalFor({s64});
+  });
+
+  // Build Instr. Make sure FMF are preserved.
+  auto FAdd =
+    B.buildInstr(TargetOpcode::G_FADD, {LLT::scalar(64)}, {Copies[0], Copies[1]},
+                 MachineInstr::MIFlag::FmNsz);
+
+  // Should not propagate the flags of src instruction.
+  auto FNeg0 =
+    B.buildInstr(TargetOpcode::G_FNEG, {LLT::scalar(64)}, {FAdd.getReg(0)},
+                 {MachineInstr::MIFlag::FmArcp});
+
+  // Preserve the one flag.
+  auto FNeg1 =
+    B.buildInstr(TargetOpcode::G_FNEG, {LLT::scalar(64)}, {Copies[0]},
+                 MachineInstr::MIFlag::FmNoInfs);
+
+  AInfo Info(MF->getSubtarget());
+  DummyGISelObserver Observer;
+  LegalizerHelper Helper(*MF, Info, Observer, B);
+  // Perform Legalization
+  EXPECT_EQ(LegalizerHelper::LegalizeResult::Legalized,
+            Helper.lower(*FNeg0, 0, LLT::scalar(64)));
+  EXPECT_EQ(LegalizerHelper::LegalizeResult::Legalized,
+            Helper.lower(*FNeg1, 0, LLT::scalar(64)));
+
+  auto CheckStr = R"(
+  CHECK: [[FADD:%[0-9]+]]:_(s64) = nsz G_FADD %0:_, %1:_
+  CHECK: [[CONST0:%[0-9]+]]:_(s64) = G_FCONSTANT double -0.000000e+00
+  CHECK: [[FSUB0:%[0-9]+]]:_(s64) = arcp G_FSUB [[CONST0]]:_, [[FADD]]:_
+  CHECK: [[CONST1:%[0-9]+]]:_(s64) = G_FCONSTANT double -0.000000e+00
+  CHECK: [[FSUB1:%[0-9]+]]:_(s64) = ninf G_FSUB [[CONST1]]:_, %0:_
+  )";
+
+  // Check
+  EXPECT_TRUE(CheckMachineFunction(*MF, CheckStr)) << *MF;
+}
 } // namespace