[PATCH] D89513: [AArch64][GlobalISel] Select csinc if a select has a 1 on RHS.

[Amara Emerson via Phabricator via llvm-commits]

aemerson created this revision.
aemerson added a reviewer: paquette.
aemerson added a project: LLVM.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls, rovka.
aemerson requested review of this revision.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D89513

Files:
  llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir


Index: llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir
+++ llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir
@@ -97,3 +97,29 @@
     $w0 = COPY %select(s32)
     RET_ReallyLR implicit $w0
 ...
+---
+name:            csinc
+alignment:       4
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $w0, $w1
+
+    ; CHECK-LABEL: name: csinc
+    ; CHECK: liveins: $w0, $w1
+    ; CHECK: [[COPY:%[0-9]+]]:gpr32common = COPY $w0
+    ; CHECK: [[SUBSWri:%[0-9]+]]:gpr32 = SUBSWri [[COPY]], 1, 0, implicit-def $nzcv
+    ; CHECK: [[CSINCWr:%[0-9]+]]:gpr32 = CSINCWr [[COPY]], $wzr, 0, implicit $nzcv
+    ; CHECK: $w0 = COPY [[CSINCWr]]
+    ; CHECK: RET_ReallyLR implicit $w0
+    %0:gpr(s32) = COPY $w0
+    %1:gpr(s32) = COPY $w1
+    %2:gpr(s32) = G_CONSTANT i32 1
+    %5:gpr(s32) = G_ICMP intpred(eq), %0(s32), %2
+    %3:gpr(s1) = G_TRUNC %5(s32)
+    %4:gpr(s32) = G_SELECT %3(s1), %0, %2
+    $w0 = COPY %4(s32)
+    RET_ReallyLR implicit $w0
+...
Index: llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
===================================================================
--- llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -4102,7 +4102,8 @@
   MachineIRBuilder MIB(I);
   MachineRegisterInfo &MRI = *MIB.getMRI();
   const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
-
+  Register SrcReg1 = I.getOperand(2).getReg();
+  Register SrcReg2 = I.getOperand(3).getReg();
   // We want to recognize this pattern:
   //
   // $z = G_FCMP pred, $x, $y
@@ -4196,6 +4197,31 @@
   }
 
   // Emit the select.
+  // We may also be able to emit a CSINC if the RHS operand is a 1.
+  const RegisterBank &SrcRB = *RBI.getRegBank(SrcReg1, MRI, TRI);
+  auto ValAndVReg =
+      getConstantVRegValWithLookThrough(SrcReg2, MRI);
+
+  if (SrcRB.getID() == AArch64::GPRRegBankID && ValAndVReg &&
+      ValAndVReg->Value == 1) {
+    unsigned Size = MRI.getType(SrcReg1).getSizeInBits();
+    unsigned Opc = 0;
+    Register Zero;
+    if (Size == 64) {
+      Opc = AArch64::CSINCXr;
+      Zero = AArch64::XZR;
+    } else {
+      Opc = AArch64::CSINCWr;
+      Zero = AArch64::WZR;
+    }
+    auto CSINC =
+        MIB.buildInstr(Opc, {I.getOperand(0).getReg()}, {SrcReg1, Zero})
+            .addImm(CondCode);
+    constrainSelectedInstRegOperands(*CSINC, TII, TRI, RBI);
+    I.eraseFromParent();
+    return true;
+  }
+
   unsigned CSelOpc = selectSelectOpc(I, MRI, RBI);
   auto CSel =
       MIB.buildInstr(CSelOpc, {I.getOperand(0).getReg()},


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