[GlobalISel] Fix incorrect sign extension when combining G_INTTOPTR and G_PTR_ADD

The GlobalISel combiner currently uses sign extension when manipulating
the LHS constant when combining a sequence of the following sequence of
machine instructions into a single constant:
```
  %0:_(s32) = G_CONSTANT i32 <CONSTANT>
  %1:_(p0) = G_INTTOPTR %0:_(s32)
  %2:_(s64) = G_CONSTANT i64 <CONSTANT>
  %3:_(p0) = G_PTR_ADD %1:_, %2:_(s64)
```

This causes an issue when the bit width of the first contant and the
target pointer size are different, as G_INTTOPTR has no sign extension
semantics.

This patch fixes this by capture an arbitrary precision in when matching
the constant, allowing the matching function to correctly zero extend
it.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D116941

llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h

@@ -353,8 +353,8 @@ public:
                                   std::pair<Register, bool> &PtrRegAndCommute);
 
   // Transform G_PTR_ADD (G_PTRTOINT C1), C2 -> C1 + C2
-  bool matchCombineConstPtrAddToI2P(MachineInstr &MI, int64_t &NewCst);
-  void applyCombineConstPtrAddToI2P(MachineInstr &MI, int64_t &NewCst);
+  bool matchCombineConstPtrAddToI2P(MachineInstr &MI, APInt &NewCst);
+  void applyCombineConstPtrAddToI2P(MachineInstr &MI, APInt &NewCst);
 
   /// Transform anyext(trunc(x)) to x.
   bool matchCombineAnyExtTrunc(MachineInstr &MI, Register &Reg);

llvm/include/llvm/CodeGen/GlobalISel/MIPatternMatch.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_CODEGEN_GLOBALISEL_MIPATTERNMATCH_H
 #define LLVM_CODEGEN_GLOBALISEL_MIPATTERNMATCH_H
 
+#include "llvm/ADT/APInt.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/IR/InstrTypes.h"
@@ -59,11 +60,26 @@ inline OneNonDBGUse_match<SubPat> m_OneNonDBGUse(const SubPat &SP) {
   return SP;
 }
 
-struct ConstantMatch {
-  int64_t &CR;
-  ConstantMatch(int64_t &C) : CR(C) {}
+template <typename ConstT>
+inline Optional<ConstT> matchConstant(Register, const MachineRegisterInfo &);
+
+template <>
+inline Optional<APInt> matchConstant(Register Reg,
+                                     const MachineRegisterInfo &MRI) {
+  return getIConstantVRegVal(Reg, MRI);
+}
+
+template <>
+inline Optional<int64_t> matchConstant(Register Reg,
+                                       const MachineRegisterInfo &MRI) {
+  return getIConstantVRegSExtVal(Reg, MRI);
+}
+
+template <typename ConstT> struct ConstantMatch {
+  ConstT &CR;
+  ConstantMatch(ConstT &C) : CR(C) {}
   bool match(const MachineRegisterInfo &MRI, Register Reg) {
-    if (auto MaybeCst = getIConstantVRegSExtVal(Reg, MRI)) {
+    if (auto MaybeCst = matchConstant<ConstT>(Reg, MRI)) {
       CR = *MaybeCst;
       return true;
     }
@@ -71,7 +87,12 @@ struct ConstantMatch {
   }
 };
 
-inline ConstantMatch m_ICst(int64_t &Cst) { return ConstantMatch(Cst); }
+inline ConstantMatch<APInt> m_ICst(APInt &Cst) {
+  return ConstantMatch<APInt>(Cst);
+}
+inline ConstantMatch<int64_t> m_ICst(int64_t &Cst) {
+  return ConstantMatch<int64_t>(Cst);
+}
 
 struct GCstAndRegMatch {
   Optional<ValueAndVReg> &ValReg;

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

@@ -391,7 +391,7 @@ def add_p2i_to_ptradd : GICombineRule<
 >;
 
 // Fold (ptr_add (int2ptr C1), C2) -> C1 + C2
-def const_ptradd_to_i2p_matchinfo : GIDefMatchData<"int64_t">;
+def const_ptradd_to_i2p_matchinfo : GIDefMatchData<"APInt">;
 def const_ptradd_to_i2p: GICombineRule<
   (defs root:$root, const_ptradd_to_i2p_matchinfo:$info),
   (match (wip_match_opcode G_PTR_ADD):$root,

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -2025,16 +2025,19 @@ void CombinerHelper::applyCombineAddP2IToPtrAdd(
 }
 
 bool CombinerHelper::matchCombineConstPtrAddToI2P(MachineInstr &MI,
-                                                  int64_t &NewCst) {
+                                                  APInt &NewCst) {
   auto &PtrAdd = cast<GPtrAdd>(MI);
   Register LHS = PtrAdd.getBaseReg();
   Register RHS = PtrAdd.getOffsetReg();
   MachineRegisterInfo &MRI = Builder.getMF().getRegInfo();
 
-  if (auto RHSCst = getIConstantVRegSExtVal(RHS, MRI)) {
-    int64_t Cst;
+  if (auto RHSCst = getIConstantVRegVal(RHS, MRI)) {
+    APInt Cst;
     if (mi_match(LHS, MRI, m_GIntToPtr(m_ICst(Cst)))) {
-      NewCst = Cst + *RHSCst;
+      auto DstTy = MRI.getType(PtrAdd.getReg(0));
+      // G_INTTOPTR uses zero-extension
+      NewCst = Cst.zextOrTrunc(DstTy.getSizeInBits());
+      NewCst += RHSCst->sextOrTrunc(DstTy.getSizeInBits());
       return true;
     }
   }
@@ -2043,7 +2046,7 @@ bool CombinerHelper::matchCombineConstPtrAddToI2P(MachineInstr &MI,
 }
 
 void CombinerHelper::applyCombineConstPtrAddToI2P(MachineInstr &MI,
-                                                  int64_t &NewCst) {
+                                                  APInt &NewCst) {
   auto &PtrAdd = cast<GPtrAdd>(MI);
   Register Dst = PtrAdd.getReg(0);
 

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

@@ -50,3 +50,18 @@ body:             |
     %4:_(s64) = G_PTRTOINT %3
     $x0 = COPY %4(s64)
 ...
+---
+name:            test_combine_zero_extend
+body:             |
+  bb.1:
+  liveins: $x0
+
+    ; CHECK-LABEL: name: test_combine_zero_extend
+    ; CHECK: [[C:%[0-9]+]]:_(p0) = G_CONSTANT i64 4291891236
+    ; CHECK-NEXT: $x0 = COPY [[C]](p0)
+    %0:_(s32) = G_CONSTANT i32 -3076096
+    %1:_(p0) = G_INTTOPTR %0:_(s32)
+    %2:_(s64) = G_CONSTANT i64 36
+    %3:_(p0) = G_PTR_ADD %1:_, %2:_(s64)
+    $x0 = COPY %3
+...

llvm/test/CodeGen/AArch64/GlobalISel/inttoptr_add.ll

@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64-none-eabi -global-isel -verify-machineinstrs %s -o - | FileCheck %s
+
+define dso_local void @fn() {
+; CHECK-LABEL: fn:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mov x8, #4132
+; CHECK-NEXT:    mov w9, #1
+; CHECK-NEXT:    movk x8, #65489, lsl #16
+; CHECK-NEXT:    str w9, [x8]
+; CHECK-NEXT:    ret
+entry:
+  store i32 1, i32* bitcast (i8* getelementptr inbounds (i8, i8* inttoptr (i32 -3076096 to i8*), i64 36) to i32*), align 4
+  ret void
+}