[llvm] 4ad4599 - [AArch64][GlobalISel] Select csinc if a select has a 1 on RHS.

[Amara Emerson via llvm-commits]

Author: Amara Emerson
Date: 2020-10-16T16:49:52-07:00
New Revision: 4ad459997e65fc97427a10b37123b7e0fed1931f

URL: https://github.com/llvm/llvm-project/commit/4ad459997e65fc97427a10b37123b7e0fed1931f
DIFF: https://github.com/llvm/llvm-project/commit/4ad459997e65fc97427a10b37123b7e0fed1931f.diff

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

Differential Revision: https://reviews.llvm.org/D89513

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
index f7de686ab60f..7aef76edb4a9 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -4119,7 +4119,8 @@ bool AArch64InstructionSelector::tryOptSelect(MachineInstr &I) const {
   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
@@ -4208,6 +4209,31 @@ bool AArch64InstructionSelector::tryOptSelect(MachineInstr &I) const {
   }
 
   // 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()},

diff  --git a/llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir b/llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir
index 0bef7fd48b45..9ccb42010736 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/fold-select.mir
@@ -97,3 +97,29 @@ body:             |
     $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
+...