[GlobalISel] Constant-fold G_PTR_ADD with different type sizes (#81473)

All other opcodes in the list are constrained to have the same type on
both operands, but not G_PTR_ADD.

Fixes  #81464

Author: Pierre-vh

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -660,8 +660,11 @@ std::optional<APInt> llvm::ConstantFoldBinOp(unsigned Opcode,
   default:
     break;
   case TargetOpcode::G_ADD:
-  case TargetOpcode::G_PTR_ADD:
     return C1 + C2;
+  case TargetOpcode::G_PTR_ADD:
+    // Types can be of different width here.
+    // Result needs to be the same width as C1, so trunc or sext C2.
+    return C1 + C2.sextOrTrunc(C1.getBitWidth());
   case TargetOpcode::G_AND:
     return C1 & C2;
   case TargetOpcode::G_ASHR:

llvm/test/CodeGen/AMDGPU/GlobalISel/combine-extract-vector-load.mir

@@ -0,0 +1,40 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=amdgcn -run-pass=amdgpu-prelegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s
+
+# Tries to emit a foldable G_PTR_ADD with (p1, s32) operands.
+---
+name:            test_ptradd_crash__offset_smaller
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    ; CHECK-LABEL: name: test_ptradd_crash__offset_smaller
+    ; CHECK: [[C:%[0-9]+]]:_(p1) = G_CONSTANT i64 12
+    ; CHECK-NEXT: [[LOAD:%[0-9]+]]:_(s32) = G_LOAD [[C]](p1) :: (load (s32), addrspace 1)
+    ; CHECK-NEXT: $sgpr0 = COPY [[LOAD]](s32)
+    ; CHECK-NEXT: SI_RETURN_TO_EPILOG implicit $sgpr0
+    %1:_(p1) = G_CONSTANT i64 0
+    %3:_(s32) = G_CONSTANT i32 3
+    %0:_(<4 x s32>) = G_LOAD %1 :: (load (<4 x s32>) from `ptr addrspace(1) null`, addrspace 1)
+    %2:_(s32) = G_EXTRACT_VECTOR_ELT %0, %3
+    $sgpr0 = COPY %2
+    SI_RETURN_TO_EPILOG implicit $sgpr0
+...
+
+# Tries to emit a foldable G_PTR_ADD with (p1, s128) operands.
+---
+name:            test_ptradd_crash__offset_wider
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    ; CHECK-LABEL: name: test_ptradd_crash__offset_wider
+    ; CHECK: [[C:%[0-9]+]]:_(p1) = G_CONSTANT i64 12
+    ; CHECK-NEXT: [[LOAD:%[0-9]+]]:_(s32) = G_LOAD [[C]](p1) :: (load (s32), addrspace 1)
+    ; CHECK-NEXT: $sgpr0 = COPY [[LOAD]](s32)
+    ; CHECK-NEXT: SI_RETURN_TO_EPILOG implicit $sgpr0
+    %1:_(p1) = G_CONSTANT i64 0
+    %3:_(s128) = G_CONSTANT i128 3
+    %0:_(<4 x s32>) = G_LOAD %1 :: (load (<4 x s32>) from `ptr addrspace(1) null`, addrspace 1)
+    %2:_(s32) = G_EXTRACT_VECTOR_ELT %0, %3
+    $sgpr0 = COPY %2
+    SI_RETURN_TO_EPILOG implicit $sgpr0
+...