[GISel] Add combine for constant G_PTR_ADD offsets.

https://reviews.llvm.org/D88865

This adds a single combine for GlobalISel to fold:

ptradd (inttoptr C1) C2
Into:

C1 + C2
Additionally, a small test for AArch64 is added.

Patch by pnappa.

include/llvm/CodeGen/GlobalISel/CombinerHelper.h

@@ -288,6 +288,10 @@ public:
   bool applyCombineAddP2IToPtrAdd(MachineInstr &MI,
                                   std::pair<Register, bool> &PtrRegAndCommute);
 
+  // Transform G_PTR_ADD (G_PTRTOINT C1), C2 -> C1 + C2
+  bool matchCombineConstPtrAddToI2P(MachineInstr &MI, int64_t &NewCst);
+  bool applyCombineConstPtrAddToI2P(MachineInstr &MI, int64_t &NewCst);
+
   /// Transform anyext(trunc(x)) to x.
   bool matchCombineAnyExtTrunc(MachineInstr &MI, Register &Reg);
   bool applyCombineAnyExtTrunc(MachineInstr &MI, Register &Reg);

include/llvm/Target/GlobalISel/Combine.td

@@ -339,6 +339,14 @@ def add_p2i_to_ptradd : GICombineRule<
   (apply [{ return Helper.applyCombineAddP2IToPtrAdd(*${root}, ${info}); }])
 >;
 
+// Fold (ptr_add (int2ptr C1), C2) -> C1 + C2
+def const_ptradd_to_i2p_matchinfo : GIDefMatchData<"int64_t">;
+def const_ptradd_to_i2p: GICombineRule<
+  (defs root:$root, const_ptradd_to_i2p_matchinfo:$info),
+  (match (wip_match_opcode G_PTR_ADD):$root,
+    [{ return Helper.matchCombineConstPtrAddToI2P(*${root}, ${info}); }]),
+  (apply [{ return Helper.applyCombineConstPtrAddToI2P(*${root}, ${info}); }])
+>;
 
 // Simplify: (logic_op (op x...), (op y...)) -> (op (logic_op x, y))
 def hoist_logic_op_with_same_opcode_hands: GICombineRule <
@@ -512,6 +520,8 @@ def identity_combines : GICombineGroup<[select_same_val, right_identity_zero,
                                         i2p_to_p2i, anyext_trunc_fold,
                                         fneg_fneg_fold, right_identity_one]>;
 
+def const_combines : GICombineGroup<[constant_fp_op, const_ptradd_to_i2p]>;
+
 def known_bits_simplifications : GICombineGroup<[
   and_trivial_mask, redundant_sext_inreg]>;
 
@@ -532,4 +542,4 @@ def all_combines : GICombineGroup<[trivial_combines, ptr_add_immed_chain,
     not_cmp_fold, opt_brcond_by_inverting_cond,
     unmerge_merge, fabs_fabs_fold, unmerge_cst, unmerge_dead_to_trunc,
     unmerge_zext_to_zext, trunc_ext_fold, trunc_shl,
-    constant_fp_op, xor_of_and_with_same_reg, ptr_add_with_zero]>;
+    const_combines, xor_of_and_with_same_reg, ptr_add_with_zero]>;

include/llvm/Target/GlobalISel/Combine.td.rej

@@ -0,0 +1,11 @@
+***************
+*** 532,535 ****
+      not_cmp_fold, opt_brcond_by_inverting_cond,
+      unmerge_merge, fabs_fabs_fold, unmerge_cst, unmerge_dead_to_trunc,
+      unmerge_zext_to_zext, trunc_ext_fold, trunc_shl,
+-     constant_fp_op, xor_of_and_with_same_reg]>;
+--- 542,545 ----
+      not_cmp_fold, opt_brcond_by_inverting_cond,
+      unmerge_merge, fabs_fabs_fold, unmerge_cst, unmerge_dead_to_trunc,
+      unmerge_zext_to_zext, trunc_ext_fold, trunc_shl,
++     xor_of_and_with_same_reg, const_combines]>;

lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -1999,6 +1999,35 @@ bool CombinerHelper::applyCombineAddP2IToPtrAdd(
   return true;
 }
 
+bool CombinerHelper::matchCombineConstPtrAddToI2P(MachineInstr &MI,
+                                                  int64_t &NewCst) {
+  assert(MI.getOpcode() == TargetOpcode::G_PTR_ADD && "Expected a G_PTR_ADD");
+  Register LHS = MI.getOperand(1).getReg();
+  Register RHS = MI.getOperand(2).getReg();
+  MachineRegisterInfo &MRI = Builder.getMF().getRegInfo();
+
+  if (auto RHSCst = getConstantVRegVal(RHS, MRI)) {
+    int64_t Cst;
+    if (mi_match(LHS, MRI, m_GIntToPtr(m_ICst(Cst)))) {
+      NewCst = Cst + *RHSCst;
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool CombinerHelper::applyCombineConstPtrAddToI2P(MachineInstr &MI,
+                                                  int64_t &NewCst) {
+  assert(MI.getOpcode() == TargetOpcode::G_PTR_ADD && "Expected a G_PTR_ADD");
+  Register Dst = MI.getOperand(0).getReg();
+
+  Builder.setInstrAndDebugLoc(MI);
+  Builder.buildConstant(Dst, NewCst);
+  MI.eraseFromParent();
+  return true;
+}
+
 bool CombinerHelper::matchCombineAnyExtTrunc(MachineInstr &MI, Register &Reg) {
   assert(MI.getOpcode() == TargetOpcode::G_ANYEXT && "Expected a G_ANYEXT");
   Register DstReg = MI.getOperand(0).getReg();

test/CodeGen/AArch64/GlobalISel/combine-ptradd-int2ptr.mir

@@ -0,0 +1,52 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs -mtriple aarch64-unknown-unknown %s -o - | FileCheck %s
+# RUN: llc -debugify-and-strip-all-safe -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs -mtriple aarch64-unknown-unknown %s -o - | FileCheck %s
+
+---
+name:            agc.test_combine_ptradd_constants_intres
+body:             |
+  bb.1:
+    liveins: $x0
+    ; CHECK-LABEL: name: agc.test_combine_ptradd_constants_intres
+    ; CHECK: [[C:%[0-9]+]]:_(p64) = G_CONSTANT i64 44
+    ; CHECK: [[PTRTOINT:%[0-9]+]]:_(s64) = G_PTRTOINT [[C]](p64)
+    ; CHECK: $x0 = COPY [[PTRTOINT]](s64)
+    %1:_(s32) = G_CONSTANT i32 42
+    %2:_(s32) = G_CONSTANT i32 2
+    %3:_(p64) = G_INTTOPTR %2
+    %4:_(p64) = G_PTR_ADD %3, %1
+    %5:_(s64) = G_PTRTOINT %4
+    $x0 = COPY %5(s64)
+...
+---
+name:            agc.test_combine_ptradd_constants_ptrres
+body:             |
+  bb.1:
+    liveins: $x0
+    ; CHECK-LABEL: name: agc.test_combine_ptradd_constants_ptrres
+    ; CHECK: [[C:%[0-9]+]]:_(p64) = G_CONSTANT i64 44
+    ; CHECK: $x0 = COPY [[C]](p64)
+    %1:_(s32) = G_CONSTANT i32 42
+    %2:_(s32) = G_CONSTANT i32 2
+    %3:_(p64) = G_INTTOPTR %2
+    %4:_(p64) = G_PTR_ADD %3, %1
+    $x0 = COPY %4(p64)
+...
+---
+name:            agc.test_not_combine_variable_ptradd
+body:             |
+  bb.1:
+    liveins: $x0, $x1
+    ; Ensure non-constant G_PTR_ADDs are not folded.
+    ; CHECK-LABEL: name: agc.test_not_combine_variable_ptradd
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 42
+    ; CHECK: [[COPY:%[0-9]+]]:_(p64) = COPY $x1
+    ; CHECK: [[PTR_ADD:%[0-9]+]]:_(p64) = G_PTR_ADD [[COPY]], [[C]](s32)
+    ; CHECK: [[PTRTOINT:%[0-9]+]]:_(s64) = G_PTRTOINT [[PTR_ADD]](p64)
+    ; CHECK: $x0 = COPY [[PTRTOINT]](s64)
+    %1:_(s32) = G_CONSTANT i32 42
+    %2:_(p64) = COPY $x1
+    %3:_(p64) = G_PTR_ADD %2, %1
+    %4:_(s64) = G_PTRTOINT %3
+    $x0 = COPY %4(s64)
+...