[llvm] [SPIR-V] Coalesce chains of spv_gep into a single access chain (PR #194011)

[Dmitry Sidorov via llvm-commits]

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@@ -0,0 +1,80 @@
+; RUN: llc -verify-machineinstrs -O0 -mtriple=spirv-pc-vulkan1.3-library %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv-pc-vulkan1.3-library %s -o - -filetype=obj | spirv-val %}
+
+%struct.Inner = type { i32, <4 x float> }
+%struct.Outer = type { [5 x %struct.Inner], i32 }
+
+; CHECK-DAG: %[[#float:]] = OpTypeFloat 32
+; CHECK-DAG: %[[#vec4:]] = OpTypeVector %[[#float]] 4
+; CHECK-DAG: %[[#int:]] = OpTypeInt 32 0
+; CHECK-DAG: %[[#Inner:]] = OpTypeStruct %[[#int]] %[[#vec4]]
+; CHECK-DAG: %[[#idx_5:]] = OpConstant %[[#int]] 5
+; CHECK-DAG: %[[#Array:]] = OpTypeArray %[[#Inner]] %[[#idx_5]]
+; CHECK-DAG: %[[#Outer:]] = OpTypeStruct %[[#Array]] %[[#int]]
+; CHECK-DAG: %[[#ptr_Outer:]] = OpTypePointer Function %[[#Outer]]
+; CHECK-DAG: %[[#ptr_float:]] = OpTypePointer Function %[[#float]]
+; CHECK-DAG: %[[#int_0:]] = OpConstant %[[#int]] 0
+; CHECK-DAG: %[[#int_1:]] = OpConstant %[[#int]] 1
+; CHECK-DAG: %[[#int_2:]] = OpConstant %[[#int]] 2
+
+define spir_func float @two_deep(ptr %obj) convergent {
+entry:
+  %tok = call token @llvm.experimental.convergence.entry()
+  ; CHECK: %[[#obj2:]] = OpFunctionParameter %[[#ptr_Outer]]
+  ; CHECK: %[[#ptr2:]] = OpInBoundsAccessChain %[[#ptr_float]] %[[#obj2]] %[[#int_0]] %[[#int_2]] %[[#int_1]] %[[#int_1]]
+  ; CHECK-NOT: OpInBoundsAccessChain
+  ; CHECK: OpLoad %[[#float]] %[[#ptr2]]
+  %inner = getelementptr inbounds %struct.Outer, ptr %obj, i32 0, i32 0, i32 2
+  %vecp = getelementptr inbounds %struct.Inner, ptr %inner, i32 0, i32 1
+  %eltp = getelementptr inbounds <4 x float>, ptr %vecp, i32 0, i32 1
+  %val = load float, ptr %eltp, align 4
+  ret float %val
+}
+
+define spir_func float @three_deep(ptr %obj) convergent {
+entry:
+  %tok = call token @llvm.experimental.convergence.entry()
+  ; CHECK: %[[#obj3:]] = OpFunctionParameter %[[#ptr_Outer]]
+  ; CHECK: %[[#ptr3:]] = OpInBoundsAccessChain %[[#ptr_float]] %[[#obj3]] %[[#int_0]] %[[#int_2]] %[[#int_1]] %[[#int_1]]
+  ; CHECK-NOT: OpInBoundsAccessChain
+  ; CHECK: OpLoad %[[#float]] %[[#ptr3]]
+  %a = getelementptr inbounds %struct.Outer, ptr %obj, i32 0, i32 0
+  %b = getelementptr inbounds [5 x %struct.Inner], ptr %a, i32 0, i32 2
+  %c = getelementptr inbounds %struct.Inner, ptr %b, i32 0, i32 1
+  %d = getelementptr inbounds <4 x float>, ptr %c, i32 0, i32 1
+  %val = load float, ptr %d, align 4
+  ret float %val
+}
+
+; If the inner GEP has multiple uses, do NOT coalesce: emit two access chains.
+define spir_func float @inner_multi_use(ptr %obj) convergent {
+entry:
+  %tok = call token @llvm.experimental.convergence.entry()
+  ; CHECK: %[[#objm:]] = OpFunctionParameter %[[#ptr_Outer]]
+  ; CHECK: %[[#innerp:]] = OpInBoundsAccessChain {{%[0-9]+}} %[[#objm]] %[[#int_0]] %[[#int_2]] %[[#int_1]]
+  ; CHECK: %[[#eltp:]] = OpInBoundsAccessChain %[[#ptr_float]] %[[#innerp]] %[[#int_1]]
+  ; CHECK: OpStore %[[#innerp]]
+  %inner = getelementptr inbounds %struct.Outer, ptr %obj, i32 0, i32 0, i32 2, i32 1
+  %eltp = getelementptr inbounds <4 x float>, ptr %inner, i32 0, i32 1
+  store <4 x float> zeroinitializer, ptr %inner, align 16
+  %val = load float, ptr %eltp, align 4
+  ret float %val
+}
+
+; If any index is dynamic (non-constant), do NOT coalesce.
----------------
MrSidims wrote:

```suggestion
; If any index is dynamic, do NOT coalesce.
```

https://github.com/llvm/llvm-project/pull/194011