[llvm] [AMDGPU] add s_bitset[10]_b32 optimization for shl+[or, andn2] pattern (PR #134155)

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -534,6 +535,56 @@ bool SIShrinkInstructions::shrinkScalarLogicOp(MachineInstr &MI) const {
   MachineOperand *SrcReg = Src0;
   MachineOperand *SrcImm = Src1;
 
+  //  case 1:
+  //  From:
+  //  s_lshl_b32 s1, 1, s1
+  //  s_or_b32 s0, s0, s1
+  //  To:
+  //  s_bitset1_b32 s0, s1
+  //
+  //  case 2:
+  //  s_lshl_b32 s1, 1, s1
+  //  s_andn2_b32 s0, s0, s1
+  //  To:
+  //  s_bitset0_b32 s0, s1
+  if ((MI.getOpcode() == AMDGPU::S_OR_B32 ||
+       MI.getOpcode() == AMDGPU::S_ANDN2_B32) &&
+      Src0->isReg() && Src1->isReg() && Dest->getReg() == Src0->getReg()) {
+    MachineInstr *Shl = MRI->getUniqueVRegDef(Src1->getReg());
+    if (Shl && Shl->getOpcode() == AMDGPU::S_LSHL_B32) {
+      MachineOperand &ShlDest = Shl->getOperand(0);
+      MachineOperand &ShlSrc0 = Shl->getOperand(1);
+      MachineOperand &ShlSrc1 = Shl->getOperand(2);
+      const bool IsUndef = SrcReg->isUndef();
+      const bool IsKill = SrcReg->isKill();
+      if (MI.getParent() == Shl->getParent() &&
+          MRI->hasAtMostUserInstrs(ShlDest.getReg(), 2) && ShlSrc0.isImm() &&
+          ShlSrc0.getImm() == 1 && ShlSrc1.isReg()) {
+        unsigned int NewOpc = (MI.getOpcode() == AMDGPU::S_OR_B32)
+                                  ? AMDGPU::S_BITSET1_B32
+                                  : AMDGPU::S_BITSET0_B32;
+        MI.setDesc(TII->get(NewOpc));
+        Src0->setReg(ShlSrc1.getReg());
+        MI.getOperand(2).ChangeToRegister(Dest->getReg(), /*IsDef*/ false,
+                                          /*isImp*/ false, IsKill,
+                                          /*isDead*/ false, IsUndef);
+        MI.tieOperands(0, 2);
+        for (auto IE = MI.getIterator(), I = std::next(Shl->getIterator());
+             I != IE; ++I) {
+          for (MachineOperand &MO : I->operands()) {
+            if (MO.isReg() && MO.getReg() == ShlSrc1.getReg()) {
+              if (MO.isKill())
+                MO.setIsKill(false);
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jmmartinez wrote:

If a kill for `ShlSrc1` is found, shouldn't we also set the kill flag on `Src0` in the new instruction ?

https://github.com/llvm/llvm-project/pull/134155