[AMDGPU][NFC] Refactor SCC optimization (#165871)

Refactor SCC optimization

---------

Signed-off-by: John Lu <[email protected]>

Author: LU-JOHN

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -10618,6 +10618,42 @@ bool SIInstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
   return false;
 }
 
+// SCC is already valid after SCCValid.
+// SCCRedefine will redefine SCC to the same value already available after
+// SCCValid. If there are no intervening SCC conflicts delete SCCRedefine and
+// update kill/dead flags if necessary.
+static bool optimizeSCC(MachineInstr *SCCValid, MachineInstr *SCCRedefine,
+                        const SIRegisterInfo &RI) {
+  MachineInstr *KillsSCC = nullptr;
+  for (MachineInstr &MI : make_range(std::next(SCCValid->getIterator()),
+                                     SCCRedefine->getIterator())) {
+    if (MI.modifiesRegister(AMDGPU::SCC, &RI))
+      return false;
+    if (MI.killsRegister(AMDGPU::SCC, &RI))
+      KillsSCC = &MI;
+  }
+  if (MachineOperand *SccDef =
+          SCCValid->findRegisterDefOperand(AMDGPU::SCC, /*TRI=*/nullptr))
+    SccDef->setIsDead(false);
+  if (KillsSCC)
+    KillsSCC->clearRegisterKills(AMDGPU::SCC, /*TRI=*/nullptr);
+  SCCRedefine->eraseFromParent();
+  return true;
+}
+
+static bool foldableSelect(const MachineInstr &Def) {
+  if (Def.getOpcode() != AMDGPU::S_CSELECT_B32 &&
+      Def.getOpcode() != AMDGPU::S_CSELECT_B64)
+    return false;
+  bool Op1IsNonZeroImm =
+      Def.getOperand(1).isImm() && Def.getOperand(1).getImm() != 0;
+  bool Op2IsZeroImm =
+      Def.getOperand(2).isImm() && Def.getOperand(2).getImm() == 0;
+  if (!Op1IsNonZeroImm || !Op2IsZeroImm)
+    return false;
+  return true;
+}
+
 bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
                                        Register SrcReg2, int64_t CmpMask,
                                        int64_t CmpValue,
@@ -10637,19 +10673,6 @@ bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
     if (!Def || Def->getParent() != CmpInstr.getParent())
       return false;
 
-    const auto foldableSelect = [](MachineInstr *Def) -> bool {
-      if (Def->getOpcode() == AMDGPU::S_CSELECT_B32 ||
-          Def->getOpcode() == AMDGPU::S_CSELECT_B64) {
-        bool Op1IsNonZeroImm =
-            Def->getOperand(1).isImm() && Def->getOperand(1).getImm() != 0;
-        bool Op2IsZeroImm =
-            Def->getOperand(2).isImm() && Def->getOperand(2).getImm() == 0;
-        if (Op1IsNonZeroImm && Op2IsZeroImm)
-          return true;
-      }
-      return false;
-    };
-
     // For S_OP that set SCC = DST!=0, do the transformation
     //
     //   s_cmp_lg_* (S_OP ...), 0 => (S_OP ...)
@@ -10660,24 +10683,12 @@ bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
     //
     //   s_cmp_lg_* (S_CSELECT* (non-zero imm), 0), 0 => (S_CSELECT* (non-zero
     //   imm), 0)
-    if (!setsSCCifResultIsNonZero(*Def) && !foldableSelect(Def))
+    if (!setsSCCifResultIsNonZero(*Def) && !foldableSelect(*Def))
       return false;
 
-    MachineInstr *KillsSCC = nullptr;
-    for (MachineInstr &MI :
-         make_range(std::next(Def->getIterator()), CmpInstr.getIterator())) {
-      if (MI.modifiesRegister(AMDGPU::SCC, &RI))
-        return false;
-      if (MI.killsRegister(AMDGPU::SCC, &RI))
-        KillsSCC = &MI;
-    }
+    if (!optimizeSCC(Def, &CmpInstr, RI))
+      return false;
 
-    if (MachineOperand *SccDef =
-            Def->findRegisterDefOperand(AMDGPU::SCC, /*TRI=*/nullptr))
-      SccDef->setIsDead(false);
-    if (KillsSCC)
-      KillsSCC->clearRegisterKills(AMDGPU::SCC, /*TRI=*/nullptr);
-    CmpInstr.eraseFromParent();
     return true;
   };
 
@@ -10755,21 +10766,8 @@ bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
     if (IsReversedCC && !MRI->hasOneNonDBGUse(DefReg))
       return false;
 
-    MachineInstr *KillsSCC = nullptr;
-    for (MachineInstr &MI :
-         make_range(std::next(Def->getIterator()), CmpInstr.getIterator())) {
-      if (MI.modifiesRegister(AMDGPU::SCC, &RI))
-        return false;
-      if (MI.killsRegister(AMDGPU::SCC, &RI))
-        KillsSCC = &MI;
-    }
-
-    MachineOperand *SccDef =
-        Def->findRegisterDefOperand(AMDGPU::SCC, /*TRI=*/nullptr);
-    SccDef->setIsDead(false);
-    if (KillsSCC)
-      KillsSCC->clearRegisterKills(AMDGPU::SCC, /*TRI=*/nullptr);
-    CmpInstr.eraseFromParent();
+    if (!optimizeSCC(Def, &CmpInstr, RI))
+      return false;
 
     if (!MRI->use_nodbg_empty(DefReg)) {
       assert(!IsReversedCC);