[SPIR-V] Add spv.gep support for ptrcast legal (#134388)

Adds support the the spv.gep intrinsic to the spv ptrcast legalization
step. Those intrinsics are generated by the backend thus not directly
visible in the tests.
This is a pre-requisite to implement addrspacecast legalization for
logical SPIR-V.

Author: Keenuts

llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp

@@ -170,6 +170,12 @@ class SPIRVLegalizePointerCast : public FunctionPass {
           DeadInstructions.push_back(Intrin);
           continue;
         }
+
+        if (Intrin->getIntrinsicID() == Intrinsic::spv_gep) {
+          GR->replaceAllUsesWith(CastedOperand, OriginalOperand,
+                                 /* DeleteOld= */ false);
+          continue;
+        }
       }
 
       llvm_unreachable("Unsupported ptrcast user. Please fix.");

llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-struct.ll

@@ -0,0 +1,47 @@
+; RUN: llc -verify-machineinstrs -O0 -mtriple=spirv-unknown-vulkan-compute %s -o - | FileCheck %s --match-full-lines
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv-unknown-vulkan %s -o - -filetype=obj | spirv-val %}
+
+; CHECK-DAG:       %[[#uint:]] = OpTypeInt 32 0
+; CHECK-DAG:     %[[#uint64:]] = OpTypeInt 64 0
+; CHECK-DAG:    %[[#uint_pp:]] = OpTypePointer Private %[[#uint]]
+; CHECK-DAG:     %[[#uint_0:]] = OpConstant %[[#uint]] 0
+; CHECK-DAG:     %[[#uint_1:]] = OpConstant %[[#uint]] 1
+; CHECK-DAG:    %[[#uint_10:]] = OpConstant %[[#uint]] 10
+; CHECK-DAG:    %[[#t_array:]] = OpTypeArray %[[#uint]] %[[#uint_10]]
+; CHECK-DAG:       %[[#t_s1:]] = OpTypeStruct %[[#t_array]]
+; CHECK-DAG:       %[[#t_s2_s_a_s:]] = OpTypeStruct %[[#uint]] %[[#uint]]
+; CHECK-DAG:       %[[#t_s2_s_a:]] = OpTypeArray %[[#t_s2_s_a_s]] %[[#uint_10]]
+; CHECK-DAG:       %[[#t_s2_s:]] = OpTypeStruct %[[#t_s2_s_a]]
+; CHECK-DAG:       %[[#t_s2:]] = OpTypeStruct %[[#t_s2_s]] %[[#uint]]
+; CHECK-DAG:     %[[#null_s1:]] = OpConstantNull %[[#t_s1]]
+; CHECK-DAG:     %[[#null_s2:]] = OpConstantNull %[[#t_s2]]
+; CHECK-DAG:  %[[#ptr_s1:]] = OpTypePointer Private %[[#t_s1]]
+; CHECK-DAG:  %[[#ptr_s2:]] = OpTypePointer Private %[[#t_s2]]
+
+%S1 = type { [10 x i32] }
+%S2 = type { { [10 x { i32, i32 } ] }, i32 }
+
+; CHECK-DAG: %[[#global1:]] = OpVariable %[[#ptr_s1]] Private %[[#null_s1]]
+@global1 = internal addrspace(10) global %S1 zeroinitializer
+; CHECK-DAG: %[[#global2:]] = OpVariable %[[#ptr_s2]] Private %[[#null_s2]]
+@global2 = internal addrspace(10) global %S2 zeroinitializer
+
+define spir_func noundef i32 @foo(i64 noundef %index) local_unnamed_addr {
+; CHECK: %[[#index:]] = OpFunctionParameter %[[#uint64]]
+entry:
+; CHECK: %[[#ptr:]] = OpInBoundsAccessChain %[[#uint_pp]] %[[#global1]] %[[#uint_0]] %[[#index]]
+  %ptr = getelementptr inbounds %S1, ptr addrspace(10) @global1, i64 0, i32 0, i64 %index
+; CHECK: %[[#val:]] = OpLoad %[[#uint]] %[[#ptr]] Aligned 4
+  %val = load i32, ptr addrspace(10) %ptr
+  ret i32 %val
+}
+
+define spir_func noundef i32 @bar(i64 noundef %index) local_unnamed_addr {
+; CHECK: %[[#index:]] = OpFunctionParameter %[[#uint64]]
+entry:
+; CHECK: %[[#ptr:]] = OpInBoundsAccessChain %[[#uint_pp]] %[[#global2]] %[[#uint_0]] %[[#uint_0]] %[[#index]] %[[#uint_1]]
+  %ptr = getelementptr inbounds %S2, ptr addrspace(10) @global2, i64 0, i32 0, i32 0, i64 %index, i32 1
+; CHECK: %[[#val:]] = OpLoad %[[#uint]] %[[#ptr]] Aligned 4
+  %val = load i32, ptr addrspace(10) %ptr
+  ret i32 %val
+}