[opt] Fix pointer stores in DCE (KhronosGroup#5739)

When a trying to mark store that use the same address as a load live, we
consider any use of the pointer in the store instruction enough to make
the store live. This is not correct. We should only mark the store as
live if it store to the pointer, and not storing the pointer to another
memory location.

This causes DCE to miss some dead code.

Author: s-perron

source/opt/aggressive_dead_code_elim_pass.cpp

@@ -134,7 +134,12 @@ void AggressiveDCEPass::AddStores(Function* func, uint32_t ptrId) {
         }
         break;
       // If default, assume it stores e.g. frexp, modf, function call
-      case spv::Op::OpStore:
+      case spv::Op::OpStore: {
+        const uint32_t kStoreTargetAddrInIdx = 0;
+        if (user->GetSingleWordInOperand(kStoreTargetAddrInIdx) == ptrId)
+          AddToWorklist(user);
+        break;
+      }
       default:
         AddToWorklist(user);
         break;

test/opt/aggressive_dead_code_elim_test.cpp

@@ -7992,6 +7992,83 @@ OpFunctionEnd
   SinglePassRunAndCheck<AggressiveDCEPass>(test, test, true, true);
 }
 
+TEST_F(AggressiveDCETest, StoringAPointer) {
+  // A store that stores a pointer should not be kept live because the value
+  // being stored is eventually loaded from.
+
+  const std::string text = R"(
+               OpCapability CooperativeMatrixKHR
+               OpCapability Shader
+               OpExtension "SPV_KHR_cooperative_matrix"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint GLCompute %1 "main" %2
+               OpExecutionMode %1 LocalSize 64 1 1
+               OpSource HLSL 600
+               OpDecorate %2 DescriptorSet 0
+               OpDecorate %2 Binding 0
+               OpDecorate %_runtimearr_int ArrayStride 4
+               OpMemberDecorate %_struct_4 0 Offset 0
+               OpDecorate %_struct_4 Block
+        %int = OpTypeInt 32 1
+      %int_0 = OpConstant %int 0
+      %int_1 = OpConstant %int 1
+       %uint = OpTypeInt 32 0
+     %uint_0 = OpConstant %uint 0
+    %uint_64 = OpConstant %uint 64
+     %uint_3 = OpConstant %uint 3
+    %uint_16 = OpConstant %uint 16
+     %uint_4 = OpConstant %uint 4
+%_runtimearr_int = OpTypeRuntimeArray %int
+  %_struct_4 = OpTypeStruct %_runtimearr_int
+%_ptr_StorageBuffer__struct_4 = OpTypePointer StorageBuffer %_struct_4
+       %void = OpTypeVoid
+         %16 = OpTypeFunction %void
+; CHECK: [[mat:%\w+]] = OpTypeCooperativeMatrixKHR %int %uint_3 %uint_16 %uint_4 %uint_0
+         %17 = OpTypeCooperativeMatrixKHR %int %uint_3 %uint_16 %uint_4 %uint_0
+; CHECK: [[struct:%\w+]] = OpTypeStruct [[mat]]
+ %_struct_18 = OpTypeStruct %17
+; CHECK: [[ptr:%\w+]] = OpTypePointer Function [[struct]]
+%_ptr_Function__struct_18 = OpTypePointer Function %_struct_18
+%_ptr_StorageBuffer_int = OpTypePointer StorageBuffer %int
+%_ptr_Function_17 = OpTypePointer Function %17
+%_ptr_Function_int = OpTypePointer Function %int
+%_ptr_Function__ptr_Function_int = OpTypePointer Function %_ptr_Function_int
+          %2 = OpVariable %_ptr_StorageBuffer__struct_4 StorageBuffer
+
+; The stored to the fist two variables should be removed and the variables
+; as well. The only function scope variable should be the cooperative matrix.
+; CHECK: OpFunction
+; CHECK-NOT: OpVariable %_ptr_Function__ptr_Function_int Function
+; CHECK: OpVariable [[ptr]] Function
+; CHECK-NOT: OpVariable
+          %1 = OpFunction %void None %16
+         %24 = OpLabel
+         %25 = OpVariable %_ptr_Function__ptr_Function_int Function
+         %26 = OpVariable %_ptr_Function__ptr_Function_int Function
+         %27 = OpVariable %_ptr_Function__struct_18 Function
+         %28 = OpAccessChain %_ptr_StorageBuffer_int %2 %int_0 %uint_0
+         %29 = OpCooperativeMatrixLoadKHR %17 %28 %int_1
+         %30 = OpCompositeConstruct %_struct_18 %29
+               OpStore %27 %30
+         %31 = OpAccessChain %_ptr_Function_17 %27 %int_0
+         %32 = OpAccessChain %_ptr_Function_int %27 %int_0 %uint_0
+               OpStore %26 %32
+         %33 = OpLoad %int %32
+         %34 = OpIAdd %int %33 %int_1
+               OpStore %25 %32
+               OpStore %32 %34
+         %35 = OpAccessChain %_ptr_StorageBuffer_int %2 %int_0 %uint_64
+         %36 = OpLoad %17 %31
+               OpCooperativeMatrixStoreKHR %35 %36 %int_0
+               OpReturn
+               OpFunctionEnd
+)";
+
+  // For physical storage buffer support
+  SetTargetEnv(SPV_ENV_VULKAN_1_2);
+  SinglePassRunAndMatch<AggressiveDCEPass>(text, true);
+}
+
 }  // namespace
 }  // namespace opt
 }  // namespace spvtools