AMDGPU/GlobalISel: Legalize FDIV64

Reviewers: arsenm

Reviewed By: arsenm

Subscribers: kzhuravl, jvesely, wdng, nhaehnle, yaxunl, rovka, dstuttard, tpr, t-tye, hiraditya, Petar.Avramovic, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70403

Author: kerbowa

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

@@ -1867,6 +1867,7 @@ bool AMDGPULegalizerInfo::legalizeFDIV(MachineInstr &MI,
   LLT DstTy = MRI.getType(Dst);
   LLT S16 = LLT::scalar(16);
   LLT S32 = LLT::scalar(32);
+  LLT S64 = LLT::scalar(64);
 
   if (legalizeFastUnsafeFDIV(MI, MRI, B))
     return true;
@@ -1875,6 +1876,8 @@ bool AMDGPULegalizerInfo::legalizeFDIV(MachineInstr &MI,
     return legalizeFDIV16(MI, MRI, B);
   if (DstTy == S32)
     return legalizeFDIV32(MI, MRI, B);
+  if (DstTy == S64)
+    return legalizeFDIV64(MI, MRI, B);
 
   return false;
 }
@@ -2072,6 +2075,88 @@ bool AMDGPULegalizerInfo::legalizeFDIV32(MachineInstr &MI,
   return true;
 }
 
+bool AMDGPULegalizerInfo::legalizeFDIV64(MachineInstr &MI,
+                                         MachineRegisterInfo &MRI,
+                                         MachineIRBuilder &B) const {
+  B.setInstr(MI);
+  Register Res = MI.getOperand(0).getReg();
+  Register LHS = MI.getOperand(1).getReg();
+  Register RHS = MI.getOperand(2).getReg();
+
+  uint16_t Flags = MI.getFlags();
+
+  LLT S64 = LLT::scalar(64);
+  LLT S1 = LLT::scalar(1);
+
+  auto One = B.buildFConstant(S64, 1.0);
+
+  auto DivScale0 = B.buildIntrinsic(Intrinsic::amdgcn_div_scale, {S64, S1}, false)
+    .addUse(RHS)
+    .addUse(RHS)
+    .addUse(LHS)
+    .setMIFlags(Flags);
+
+  auto NegDivScale0 = B.buildFNeg(S64, DivScale0.getReg(0), Flags);
+
+  auto Rcp = B.buildIntrinsic(Intrinsic::amdgcn_rcp, {S64}, false)
+    .addUse(DivScale0.getReg(0))
+    .setMIFlags(Flags);
+
+  auto Fma0 = B.buildFMA(S64, NegDivScale0, Rcp, One, Flags);
+  auto Fma1 = B.buildFMA(S64, Rcp, Fma0, Rcp, Flags);
+  auto Fma2 = B.buildFMA(S64, NegDivScale0, Fma1, One, Flags);
+
+  auto DivScale1 = B.buildIntrinsic(Intrinsic::amdgcn_div_scale, {S64, S1}, false)
+    .addUse(LHS)
+    .addUse(RHS)
+    .addUse(LHS)
+    .setMIFlags(Flags);
+
+  auto Fma3 = B.buildFMA(S64, Fma1, Fma2, Fma1, Flags);
+  auto Mul = B.buildMul(S64, DivScale1.getReg(0), Fma3, Flags);
+  auto Fma4 = B.buildFMA(S64, NegDivScale0, Mul, DivScale1.getReg(0), Flags);
+
+  Register Scale;
+  if (!ST.hasUsableDivScaleConditionOutput()) {
+    // Workaround a hardware bug on SI where the condition output from div_scale
+    // is not usable.
+
+    Scale = MRI.createGenericVirtualRegister(S1);
+
+    LLT S32 = LLT::scalar(32);
+
+    auto NumUnmerge = B.buildUnmerge(S32, LHS);
+    auto DenUnmerge = B.buildUnmerge(S32, RHS);
+    auto Scale0Unmerge = B.buildUnmerge(S32, DivScale0);
+    auto Scale1Unmerge = B.buildUnmerge(S32, DivScale1);
+
+    auto CmpNum = B.buildICmp(ICmpInst::ICMP_EQ, S1, NumUnmerge.getReg(1),
+                              Scale1Unmerge.getReg(1));
+    auto CmpDen = B.buildICmp(ICmpInst::ICMP_EQ, S1, DenUnmerge.getReg(1),
+                              Scale0Unmerge.getReg(1));
+    B.buildXor(Scale, CmpNum, CmpDen);
+  } else {
+    Scale = DivScale1.getReg(1);
+  }
+
+  auto Fmas = B.buildIntrinsic(Intrinsic::amdgcn_div_fmas, {S64}, false)
+    .addUse(Fma4.getReg(0))
+    .addUse(Fma3.getReg(0))
+    .addUse(Mul.getReg(0))
+    .addUse(Scale)
+    .setMIFlags(Flags);
+
+  B.buildIntrinsic(Intrinsic::amdgcn_div_fixup, {S64}, false)
+    .addDef(Res)
+    .addUse(Fmas.getReg(0))
+    .addUse(RHS)
+    .addUse(LHS)
+    .setMIFlags(Flags);
+
+  MI.eraseFromParent();
+  return true;
+}
+
 bool AMDGPULegalizerInfo::legalizeFDIVFastIntrin(MachineInstr &MI,
                                                  MachineRegisterInfo &MRI,
                                                  MachineIRBuilder &B) const {

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.h

@@ -90,6 +90,8 @@ class AMDGPULegalizerInfo : public LegalizerInfo {
                       MachineIRBuilder &B) const;
   bool legalizeFDIV32(MachineInstr &MI, MachineRegisterInfo &MRI,
                       MachineIRBuilder &B) const;
+  bool legalizeFDIV64(MachineInstr &MI, MachineRegisterInfo &MRI,
+                      MachineIRBuilder &B) const;
   bool legalizeFastUnsafeFDIV(MachineInstr &MI, MachineRegisterInfo &MRI,
                               MachineIRBuilder &B) const;
   bool legalizeFDIVFastIntrin(MachineInstr &MI, MachineRegisterInfo &MRI,