AMDGPU: Use hex floats instead of ugly bitcasting

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

@@ -4806,9 +4806,9 @@ bool AMDGPULegalizerInfo::legalizeFDIVFastIntrin(MachineInstr &MI,
   auto Abs = B.buildFAbs(S32, RHS, Flags);
   const APFloat C0Val(1.0f);
 
-  auto C0 = B.buildConstant(S32, 0x6f800000);
-  auto C1 = B.buildConstant(S32, 0x2f800000);
-  auto C2 = B.buildConstant(S32, llvm::bit_cast<uint32_t>(1.0f));
+  auto C0 = B.buildFConstant(S32, 0x1p+96f);
+  auto C1 = B.buildFConstant(S32, 0x1p-32f);
+  auto C2 = B.buildFConstant(S32, 1.0f);
 
   auto CmpRes = B.buildFCmp(CmpInst::FCMP_OGT, S1, Abs, C0, Flags);
   auto Sel = B.buildSelect(S32, CmpRes, C1, C2, Flags);

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -9277,10 +9277,10 @@ SDValue SITargetLowering::lowerFDIV_FAST(SDValue Op, SelectionDAG &DAG) const {
 
   SDValue r1 = DAG.getNode(ISD::FABS, SL, MVT::f32, RHS);
 
-  const APFloat K0Val(llvm::bit_cast<float>(0x6f800000));
+  const APFloat K0Val(0x1p+96f);
   const SDValue K0 = DAG.getConstantFP(K0Val, SL, MVT::f32);
 
-  const APFloat K1Val(llvm::bit_cast<float>(0x2f800000));
+  const APFloat K1Val(0x1p-32f);
   const SDValue K1 = DAG.getConstantFP(K1Val, SL, MVT::f32);
 
   const SDValue One = DAG.getConstantFP(1.0, SL, MVT::f32);

llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-intrinsic-amdgcn-fdiv-fast.mir

@@ -13,9 +13,9 @@ body: |
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
     ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
     ; CHECK-NEXT: [[FABS:%[0-9]+]]:_(s32) = G_FABS [[COPY1]]
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1870659584
-    ; CHECK-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 796917760
-    ; CHECK-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 1065353216
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_FCONSTANT float 0x45F0000000000000
+    ; CHECK-NEXT: [[C1:%[0-9]+]]:_(s32) = G_FCONSTANT float 0x3DF0000000000000
+    ; CHECK-NEXT: [[C2:%[0-9]+]]:_(s32) = G_FCONSTANT float 1.000000e+00
     ; CHECK-NEXT: [[FCMP:%[0-9]+]]:_(s1) = G_FCMP floatpred(ogt), [[FABS]](s32), [[C]]
     ; CHECK-NEXT: [[SELECT:%[0-9]+]]:_(s32) = G_SELECT [[FCMP]](s1), [[C1]], [[C2]]
     ; CHECK-NEXT: [[FMUL:%[0-9]+]]:_(s32) = G_FMUL [[COPY1]], [[SELECT]]
@@ -41,9 +41,9 @@ body: |
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
     ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
     ; CHECK-NEXT: [[FABS:%[0-9]+]]:_(s32) = nsz G_FABS [[COPY1]]
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1870659584
-    ; CHECK-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 796917760
-    ; CHECK-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 1065353216
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_FCONSTANT float 0x45F0000000000000
+    ; CHECK-NEXT: [[C1:%[0-9]+]]:_(s32) = G_FCONSTANT float 0x3DF0000000000000
+    ; CHECK-NEXT: [[C2:%[0-9]+]]:_(s32) = G_FCONSTANT float 1.000000e+00
     ; CHECK-NEXT: [[FCMP:%[0-9]+]]:_(s1) = nsz G_FCMP floatpred(ogt), [[FABS]](s32), [[C]]
     ; CHECK-NEXT: [[SELECT:%[0-9]+]]:_(s32) = nsz G_SELECT [[FCMP]](s1), [[C1]], [[C2]]
     ; CHECK-NEXT: [[FMUL:%[0-9]+]]:_(s32) = nsz G_FMUL [[COPY1]], [[SELECT]]