[llvm] [DirectX] add GEP i8 legalization (PR #142475)

[Deric C. via llvm-commits]

================
@@ -106,3 +106,57 @@ define i32 @all_imm() {
   %2 = sext i8 %1 to i32
   ret i32 %2
 }
+
+define i32 @scalar_i8_geps() {
+  ; CHECK-LABEL: define i32 @scalar_i8_geps(
+  ; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca i32, align 4
+  ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds nuw i32, ptr [[ALLOCA]], i32 0
+  ; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[GEP]], align 4
+  ; CHECK-NEXT:    ret i32 [[LOAD]]
+    %1 = alloca i8, align 4
+    %2 = getelementptr inbounds nuw i8, ptr %1, i32 0
+    %3 = load i8, ptr %2
+    %4 = sext i8 %3 to i32
+    ret i32 %4
+}
+
+define i32 @i8_geps_index0() {
+  ; CHECK-LABEL: define i32 @i8_geps_index0(
+  ; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [2 x i32], align 8
+  ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds nuw i32, ptr [[ALLOCA]], i32 0
+  ; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[GEP]], align 4
+  ; CHECK-NEXT:    ret i32 [[LOAD]]
+  %1 = alloca [2 x i32], align 8
+  %2 = getelementptr inbounds nuw i8, ptr %1, i32 0
+  %3 = load i8, ptr %2
+  %4 = sext i8 %3 to i32
+  ret i32 %4
+}
+
+define i32 @i8_geps_index1() {
+  ; CHECK-LABEL: define i32 @i8_geps_index1(
+  ; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [2 x i32], align 8
+  ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds nuw i32, ptr [[ALLOCA]], i32 1
----------------
Icohedron wrote:

I think this is causing the validation error `Explicit gep operator type does not match pointee type of pointer operand` after incorporating your change to support globals.
```
if (auto *GV = dyn_cast<GlobalVariable>(BasePtr))
      ElementType = GV->getValueType();
```

https://github.com/llvm/llvm-project/pull/142475