[AArch64][GlobalISel] Fold selects fed by G_PTR_ADD

[paquette]

Summary

Similar to the case for G_ADD.

There was a function in CTMark/pairlocalalign which was missing this case, causing GlobalISel to emit a add + csel when a csinc is all that is necessary.

https://godbolt.org/z/ax69E9

Minor code size improvements on CTMark at -Os.

llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp

auto TryFoldBinOpIntoSelect = [&Opc, Is32Bit, &CC, &MRI,
 
     // 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)))) {
+    if (mi_match(Reg, MRI,
+                 m_any_of(m_GAdd(m_Reg(MatchReg), m_SpecificICst(1)),
+                          m_GPtrAdd(m_Reg(MatchReg), m_SpecificICst(1))))) {
       Opc = Is32Bit ? AArch64::CSINCWr : AArch64::CSINCXr;
       Reg = MatchReg;
       if (Invert) {
         CC = AArch64CC::getInvertedCondCode(CC);
         std::swap(Reg, OtherReg);
       }
       return true;
     }

llvm/test/CodeGen/AArch64/GlobalISel/select-select.mir

bb.0:
     %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
 
 ...
 ---
+name:            csinc_ptr_add
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2
+    ; G_SELECT cc, %true, (G_PTR_ADD %x, 1) -> CSINC %true, %x, cc
+
+    ; CHECK-LABEL: name: csinc_ptr_add
+    ; CHECK: liveins: $x0, $x1, $x2
+    ; CHECK: %reg0:gpr64 = COPY $x0
+    ; CHECK: %reg1:gpr64 = COPY $x1
+    ; CHECK: %cond:gpr32 = COPY %reg0.sub_32
+    ; CHECK: %t:gpr64 = COPY $x2
+    ; CHECK: [[ANDSWri:%[0-9]+]]:gpr32 = ANDSWri %cond, 0, implicit-def $nzcv
+    ; CHECK: %select:gpr64 = CSINCXr %t, %reg1, 1, implicit $nzcv
+    ; CHECK: $x0 = COPY %select
+    ; CHECK: RET_ReallyLR implicit $x0
+    %reg0:gpr(s64) = COPY $x0
+    %reg1:gpr(p0) = COPY $x1
+    %cond:gpr(s1) = G_TRUNC %reg0(s64)
+    %t:gpr(p0) = COPY $x2
+    %one:gpr(s64) = G_CONSTANT i64 1
+    %ptr_add:gpr(p0) = G_PTR_ADD %reg1(p0), %one
+    %select:gpr(p0) = G_SELECT %cond(s1), %t, %ptr_add
+    $x0 = COPY %select(p0)
+    RET_ReallyLR implicit $x0
+
+...
+---
 name:            binop_dont_optimize_twice
 legalized:       true
 regBankSelected: true
 tracksRegLiveness: true
 body:             |
   bb.0:
     liveins: $w0, $w1, $w2
     ; CHECK-LABEL: name: binop_dont_optimize_twice