GlobalISel: support legalization of G_FCONSTANTs

llvm-svn: 279341

llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

@@ -302,6 +302,15 @@ public:
   MachineInstrBuilder buildIntrinsic(ArrayRef<LLT> Tys, Intrinsic::ID ID,
                                      unsigned Res, bool HasSideEffects);
 
+  /// Build and insert \p Res<def> = G_FPTRUNC \p Ty \p Op
+  ///
+  /// G_FPTRUNC converts a floating-point value into one with a smaller type.
+  ///
+  /// \pre setBasicBlock or setMI must have been called.
+  ///
+  /// \return The newly created instruction.
+  MachineInstrBuilder buildFPTrunc(LLT Ty, unsigned Res, unsigned Op);
+
   /// Build and insert \p Res<def> = G_TRUNC \p Ty \p Op
   ///
   /// G_TRUNC extracts the low bits of a type. For a vector type each element is

llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp

@@ -211,6 +211,11 @@ MachineInstrBuilder MachineIRBuilder::buildTrunc(LLT Ty, unsigned Res,
   return buildInstr(TargetOpcode::G_TRUNC, Ty).addDef(Res).addUse(Op);
 }
 
+MachineInstrBuilder MachineIRBuilder::buildFPTrunc(LLT Ty, unsigned Res,
+                                           unsigned Op) {
+  return buildInstr(TargetOpcode::G_FPTRUNC, Ty).addDef(Res).addUse(Op);
+}
+
 MachineInstrBuilder MachineIRBuilder::buildICmp(ArrayRef<LLT> Tys,
                                                 CmpInst::Predicate Pred,
                                                 unsigned Res, unsigned Op0,

llvm/lib/CodeGen/GlobalISel/MachineLegalizeHelper.cpp

@@ -141,6 +141,14 @@ MachineLegalizeHelper::widenScalar(MachineInstr &MI, LLT WideTy) {
     MI.eraseFromParent();
     return Legalized;
   }
+  case TargetOpcode::G_FCONSTANT: {
+    MIRBuilder.setInstr(MI);
+    unsigned DstExt = MRI.createGenericVirtualRegister(WideSize);
+    MIRBuilder.buildFConstant(WideTy, DstExt, *MI.getOperand(1).getFPImm());
+    MIRBuilder.buildFPTrunc(MI.getType(), MI.getOperand(0).getReg(), DstExt);
+    MI.eraseFromParent();
+    return Legalized;
+  }
   }
 }
 

llvm/lib/Target/AArch64/AArch64MachineLegalizer.cpp

@@ -63,6 +63,7 @@ AArch64MachineLegalizer::AArch64MachineLegalizer() {
   for (auto Ty : {s1, s8, s16})
     setAction(TargetOpcode::G_CONSTANT, Ty, WidenScalar);
 
+  setAction(TargetOpcode::G_FCONSTANT, s16, WidenScalar);
 
   setAction(G_BR, LLT::unsized(), Legal);
 

llvm/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir

@@ -53,7 +53,10 @@ body: |
     ; CHECK-LABEL: name: test_fconstant
     ; CHECK: %0(32) = G_FCONSTANT s32  float 1.000000e+00
     ; CHECK: %1(64) = G_FCONSTANT s64  double 2.000000e+00
+    ; CHECK: [[TMP:%[0-9]+]](32) = G_FCONSTANT s32 half 0xH0000
+    ; CHECK; %2(16) = G_FPTRUNC s16 [[TMP]]
 
     %0(32) = G_FCONSTANT s32 float 1.0
     %1(64) = G_FCONSTANT s64 double 2.0
+    %2(16) = G_FCONSTANT s16 half 0.0
 ...