[SPIR-V] Add spv.gep support for ptrcast legal

[Keenuts]

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.

[llvmbot]

@llvm/pr-subscribers-backend-spir-v

Author: Nathan Gauër (Keenuts)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/134388.diff

2 Files Affected:

• (modified) llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp (+6)
• (added) llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-struct.ll (+47)

diff --git a/llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp b/llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp
index 560869f9fe62a..5ba4fbb02560d 100644
--- a/llvm/lib/Target/SPIRV/SPIRVLegalizePointerCast.cpp
+++ b/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.");
diff --git a/llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-struct.ll b/llvm/test/CodeGen/SPIRV/pointers/getelementptr-downcast-struct.ll
new file mode 100644
index 0000000000000..b0a68a30e29be
--- /dev/null
+++ b/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
+}