[AArch64][GlobalISel] Fold a chain of two G_PTR_ADDs of constant offsets.

E.g.
%addr1 = G_PTR_ADD %base, G_CONSTANT 20
%addr2 = G_PTR_ADD %addr1, G_CONSTANT 8
  -->
%addr2 = G_PTR_ADD %base, G_CONSTANT 28

Differential Revision: https://reviews.llvm.org/D72351

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index 548e2031543..3a7bf6d7378 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -1340,6 +1340,52 @@ bool CombinerHelper::tryCombineMemCpyFamily(MachineInstr &MI, unsigned MaxLen) {
   return false;
 }
 
+bool CombinerHelper::matchPtrAddImmedChain(MachineInstr &MI,
+                                           PtrAddChain &MatchInfo) {
+  // We're trying to match the following pattern:
+  //   %t1 = G_PTR_ADD %base, G_CONSTANT imm1
+  //   %root = G_PTR_ADD %t1, G_CONSTANT imm2
+  // -->
+  //   %root = G_PTR_ADD %base, G_CONSTANT (imm1 + imm2)
+
+  if (MI.getOpcode() != TargetOpcode::G_PTR_ADD)
+    return false;
+
+  Register Add2 = MI.getOperand(1).getReg();
+  Register Imm1 = MI.getOperand(2).getReg();
+  auto MaybeImmVal = getConstantVRegValWithLookThrough(Imm1, MRI);
+  if (!MaybeImmVal)
+    return false;
+
+  MachineInstr *Add2Def = MRI.getUniqueVRegDef(Add2);
+  if (!Add2Def || Add2Def->getOpcode() != TargetOpcode::G_PTR_ADD)
+    return false;
+
+  Register Base = Add2Def->getOperand(1).getReg();
+  Register Imm2 = Add2Def->getOperand(2).getReg();
+  auto MaybeImm2Val = getConstantVRegValWithLookThrough(Imm2, MRI);
+  if (!MaybeImm2Val)
+    return false;
+
+  // Pass the combined immediate to the apply function.
+  MatchInfo.Imm = MaybeImmVal->Value + MaybeImm2Val->Value;
+  MatchInfo.Base = Base;
+  return true;
+}
+
+bool CombinerHelper::applyPtrAddImmedChain(MachineInstr &MI,
+                                           PtrAddChain &MatchInfo) {
+  assert(MI.getOpcode() == TargetOpcode::G_PTR_ADD && "Expected G_PTR_ADD");
+  MachineIRBuilder MIB(MI);
+  LLT OffsetTy = MRI.getType(MI.getOperand(2).getReg());
+  auto NewOffset = MIB.buildConstant(OffsetTy, MatchInfo.Imm);
+  Observer.changingInstr(MI);
+  MI.getOperand(1).setReg(MatchInfo.Base);
+  MI.getOperand(2).setReg(NewOffset.getReg(0));
+  Observer.changedInstr(MI);
+  return true;
+}
+
 bool CombinerHelper::tryCombine(MachineInstr &MI) {
   if (tryCombineCopy(MI))
     return true;