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

[Jay Foad via llvm-commits]

================
@@ -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.
----------------
jayfoad wrote:

No strong opinion. _If_ we do anything, maybe we should enforce that the RHS has to be the width of the index size for the address space.

https://github.com/llvm/llvm-project/pull/81473