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

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -1463,9 +1463,8 @@ LegalizerHelper::lower(MachineInstr &MI, unsigned TypeIdx, LLT Ty) {
     auto Zero = MIRBuilder.buildFConstant(Ty, ZeroForNegation);
     unsigned SubByReg = MI.getOperand(1).getReg();
     unsigned ZeroReg = Zero->getOperand(0).getReg();
-    MachineInstr *SrcMI = MRI.getVRegDef(SubByReg);
     MIRBuilder.buildInstr(TargetOpcode::G_FSUB, {Res}, {ZeroReg, SubByReg},
-                          SrcMI->getFlags());
+                          MI.getFlags());
     MI.eraseFromParent();
     return Legalized;
   }

llvm/test/CodeGen/AMDGPU/GlobalISel/irtranslator-fast-math-flags.ll

@@ -0,0 +1,31 @@
+; RUN: llc -march=amdgcn -mcpu=fiji -O0 -stop-after=irtranslator -global-isel %s -o - | FileCheck %s
+
+; Check flags are preserved for a regular instruction.
+; CHECK-LABEL: name: fadd_nnan
+; CHECK: nnan G_FADD
+define amdgpu_kernel void @fadd_nnan(float %arg0, float %arg1) {
+  %res = fadd nnan float %arg0, %arg1
+  store float %res, float addrspace(1)* undef
+  ret void
+}
+
+; Check flags are preserved for a specially handled intrinsic
+; CHECK-LABEL: name: fma_fast
+; CHECK: nnan ninf nsz arcp contract afn reassoc G_FMA
+define amdgpu_kernel void @fma_fast(float %arg0, float %arg1, float %arg2) {
+  %res = call fast float @llvm.fma.f32(float %arg0, float %arg1, float %arg2)
+  store float %res, float addrspace(1)* undef
+  ret void
+}
+
+; Check flags are preserved for an arbitrarry target intrinsic
+; CHECK-LABEL: name: rcp_nsz
+; CHECK: = nsz G_INTRINSIC intrinsic(@llvm.amdgcn.rcp), %8(s32)
+define amdgpu_kernel void @rcp_nsz(float %arg0) {
+  %res = call nsz float @llvm.amdgcn.rcp.f32 (float %arg0)
+  store float %res, float addrspace(1)* undef
+  ret void
+}
+
+declare float @llvm.fma.f32(float, float, float)
+declare float @llvm.amdgcn.rcp.f32(float)

llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-fsub.mir

@@ -59,6 +59,36 @@ body: |
     $vgpr0_vgpr1 = COPY %2
 ...
 
+---
+name: test_fsub_s64_fmf
+body: |
+  bb.0:
+    liveins: $vgpr0_vgpr1, $vgpr2_vgpr3
+
+    ; SI-LABEL: name: test_fsub_s64_fmf
+    ; SI: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
+    ; SI: [[COPY1:%[0-9]+]]:_(s64) = COPY $vgpr2_vgpr3
+    ; SI: [[FNEG:%[0-9]+]]:_(s64) = G_FNEG [[COPY1]]
+    ; SI: %2:_(s64) = nnan nsz G_FADD [[COPY]], [[FNEG]]
+    ; SI: $vgpr0_vgpr1 = COPY %2(s64)
+    ; VI-LABEL: name: test_fsub_s64_fmf
+    ; VI: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
+    ; VI: [[COPY1:%[0-9]+]]:_(s64) = COPY $vgpr2_vgpr3
+    ; VI: [[FNEG:%[0-9]+]]:_(s64) = G_FNEG [[COPY1]]
+    ; VI: %2:_(s64) = nnan nsz G_FADD [[COPY]], [[FNEG]]
+    ; VI: $vgpr0_vgpr1 = COPY %2(s64)
+    ; GFX9-LABEL: name: test_fsub_s64_fmf
+    ; GFX9: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
+    ; GFX9: [[COPY1:%[0-9]+]]:_(s64) = COPY $vgpr2_vgpr3
+    ; GFX9: [[FNEG:%[0-9]+]]:_(s64) = G_FNEG [[COPY1]]
+    ; GFX9: %2:_(s64) = nnan nsz G_FADD [[COPY]], [[FNEG]]
+    ; GFX9: $vgpr0_vgpr1 = COPY %2(s64)
+    %0:_(s64) = COPY $vgpr0_vgpr1
+    %1:_(s64) = COPY $vgpr2_vgpr3
+    %2:_(s64) = nnan nsz G_FSUB %0, %1
+    $vgpr0_vgpr1 = COPY %2
+...
+
 ---
 name: test_fsub_s16
 body: |

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