[PATCH] D92868: [AArch64][GlobalISel] Fold G_SELECT cc, %t, (G_ADD %x, 1) -> CSINC %t, %x, cc

[Jessica Paquette via Phabricator via llvm-commits]

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

This implements

  G_SELECT cc, %true, (G_ADD %x, 1) -> CSINC %true, %x, cc
  G_SELECT cc, (G_ADD %x, 1), %false -> CSINC %x, %false, inv_cc

Godbolt example: https://godbolt.org/z/eoPqKq


https://reviews.llvm.org/D92868

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


Index: llvm/test/CodeGen/AArch64/GlobalISel/select-select.mir
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/select-select.mir
+++ llvm/test/CodeGen/AArch64/GlobalISel/select-select.mir
@@ -592,3 +592,61 @@
     %select:gpr(s64) = G_SELECT %cond(s1), %t, %xor
     $x0 = COPY %select(s64)
     RET_ReallyLR implicit $x0
+
+...
+---
+name:            csinc_s32
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $w0, $w1, $w2
+    ; G_SELECT cc, %true, (G_ADD %x, 1) -> CSINC %true, %x, cc
+    ; CHECK-LABEL: name: csinc_s32
+    ; CHECK: liveins: $w0, $w1, $w2
+    ; CHECK: %reg0:gpr32 = COPY $w0
+    ; CHECK: %reg1:gpr32 = COPY $w1
+    ; CHECK: %t:gpr32 = COPY $w2
+    ; CHECK: [[ANDSWri:%[0-9]+]]:gpr32 = ANDSWri %reg0, 0, implicit-def $nzcv
+    ; CHECK: %select:gpr32 = CSINCWr %t, %reg1, 1, implicit $nzcv
+    ; CHECK: $w0 = COPY %select
+    ; CHECK: RET_ReallyLR implicit $w0
+    %reg0:gpr(s32) = COPY $w0
+    %reg1:gpr(s32) = COPY $w1
+    %cond:gpr(s1) = G_TRUNC %reg0(s32)
+    %t:gpr(s32) = COPY $w2
+    %one:gpr(s32) = G_CONSTANT i32 1
+    %add:gpr(s32) = G_ADD %reg1(s32), %one
+    %select:gpr(s32) = G_SELECT %cond(s1), %t, %add
+    $w0 = COPY %select(s32)
+    RET_ReallyLR implicit $w0
+
+...
+---
+name:            csinc_s32_inverted_cc
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $w0, $w1, $w2
+    ; G_SELECT cc, (G_ADD %x, 1), %false -> CSINC %x, %false, inv_cc
+    ; CHECK-LABEL: name: csinc_s32_inverted_cc
+    ; CHECK: liveins: $w0, $w1, $w2
+    ; CHECK: %reg0:gpr32 = COPY $w0
+    ; CHECK: %reg1:gpr32 = COPY $w1
+    ; CHECK: %f:gpr32 = COPY $w2
+    ; CHECK: [[ANDSWri:%[0-9]+]]:gpr32 = ANDSWri %reg0, 0, implicit-def $nzcv
+    ; CHECK: %select:gpr32 = CSINCWr %reg1, %f, 0, implicit $nzcv
+    ; CHECK: $w0 = COPY %select
+    ; CHECK: RET_ReallyLR implicit $w0
+    %reg0:gpr(s32) = COPY $w0
+    %reg1:gpr(s32) = COPY $w1
+    %cond:gpr(s1) = G_TRUNC %reg0(s32)
+    %f:gpr(s32) = COPY $w2
+    %one:gpr(s32) = G_CONSTANT i32 1
+    %add:gpr(s32) = G_ADD %reg1(s32), %one
+    %select:gpr(s32) = G_SELECT %cond(s1), %add, %f
+    $w0 = COPY %select(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
@@ -1066,6 +1066,21 @@
       return true;
     }
 
+    // Attempt to fold:
+    //
+    // %add = G_ADD %x, 1
+    // %select = G_SELECT cc, %reg, %add
+    //
+    // Into:
+    // %select = CSINC %reg, %x, cc
+    if (mi_match(Reg, MRI, m_GAdd(m_Reg(MatchReg), m_SpecificICst(1)))) {
+      Opc = Is32Bit ? AArch64::CSINCWr : AArch64::CSINCXr;
+      Reg = MatchReg;
+      if (Invert)
+        CC = AArch64CC::getInvertedCondCode(CC);
+      return true;
+    }
+
     return false;
   };
 


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