Delete redundant s_or_b32

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

Author: LU-JOHN

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -10212,7 +10212,7 @@ static bool followSubRegDef(MachineInstr &MI,
 }
 
 MachineInstr *llvm::getVRegSubRegDef(const TargetInstrInfo::RegSubRegPair &P,
-                                     MachineRegisterInfo &MRI) {
+                                     const MachineRegisterInfo &MRI) {
   assert(MRI.isSSA());
   if (!P.Reg.isVirtual())
     return nullptr;
@@ -10748,7 +10748,31 @@ bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
   if (SrcReg2 && !getFoldableImm(SrcReg2, *MRI, CmpValue))
     return false;
 
-  const auto optimizeCmpSelect = [&CmpInstr, SrcReg, CmpValue, MRI,
+  // 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.
+  const auto optimizeSCC = [this](MachineInstr *SCCValid,
+                                  MachineInstr *SCCRedefine) -> bool {
+    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;
+  };
+
+  const auto optimizeCmpSelect = [&CmpInstr, SrcReg, CmpValue, MRI, optimizeSCC,
                                   this]() -> bool {
     if (CmpValue != 0)
       return false;
@@ -10783,25 +10807,32 @@ bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
     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))
+      return false;
 
-    if (MachineOperand *SccDef =
-            Def->findRegisterDefOperand(AMDGPU::SCC, /*TRI=*/nullptr))
-      SccDef->setIsDead(false);
-    if (KillsSCC)
-      KillsSCC->clearRegisterKills(AMDGPU::SCC, /*TRI=*/nullptr);
-    CmpInstr.eraseFromParent();
+    // If s_or_32 result is unused (i.e. it is effectively a 64-bit s_cmp_lg of
+    // a register pair) and the input is a 64-bit foldableSelect then transform:
+    //
+    //   (s_or_b32 (S_CSELECT_B64 (non-zero imm), 0), 0 => (S_CSELECT_B64
+    //   (non-zero
+    //     imm), 0)
+    if (Def->getOpcode() == AMDGPU::S_OR_B32 &&
+        MRI->use_nodbg_empty(Def->getOperand(0).getReg())) {
+      MachineOperand OrOpnd1 = Def->getOperand(1);
+      MachineOperand OrOpnd2 = Def->getOperand(2);
+
+      if (OrOpnd1.isReg() && OrOpnd2.isReg() &&
+          OrOpnd1.getReg() != OrOpnd2.getReg()) {
+        auto *Def1 = getVRegSubRegDef(getRegSubRegPair(OrOpnd1), *MRI);
+        auto *Def2 = getVRegSubRegDef(getRegSubRegPair(OrOpnd2), *MRI);
+        if (Def1 == Def2 && foldableSelect(Def1))
+          optimizeSCC(Def1, Def);
+      }
+    }
     return true;
   };
 
-  const auto optimizeCmpAnd = [&CmpInstr, SrcReg, CmpValue, MRI,
+  const auto optimizeCmpAnd = [&CmpInstr, SrcReg, CmpValue, MRI, optimizeSCC,
                                this](int64_t ExpectedValue, unsigned SrcSize,
                                      bool IsReversible, bool IsSigned) -> bool {
     // s_cmp_eq_u32 (s_and_b32 $src, 1 << n), 1 << n => s_and_b32 $src, 1 << n
@@ -10875,21 +10906,8 @@ 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))
+      return false;
 
     if (!MRI->use_nodbg_empty(DefReg)) {
       assert(!IsReversedCC);

llvm/lib/Target/AMDGPU/SIInstrInfo.h

@@ -1704,7 +1704,7 @@ TargetInstrInfo::RegSubRegPair getRegSequenceSubReg(MachineInstr &MI,
 /// skipping copy like instructions and subreg-manipulation pseudos.
 /// Following another subreg of a reg:subreg isn't supported.
 MachineInstr *getVRegSubRegDef(const TargetInstrInfo::RegSubRegPair &P,
-                               MachineRegisterInfo &MRI);
+                               const MachineRegisterInfo &MRI);
 
 /// \brief Return false if EXEC is not changed between the def of \p VReg at \p
 /// DefMI and the use at \p UseMI. Should be run on SSA. Currently does not