spirv-opt: Fix OpUndef placement in ADCE

ADCE was modifying an existing instruction in order to get the OpUndef.
This would leave the OpUndef in an invalid position. Even through it is
allowed for an OpUndef to be in a function. We are moving away from
that.

This commit create a new instruction for the OpUndef, and places it in
the right place.

Fixes KhronosGroup#6316

Author: s-perron

source/opt/aggressive_dead_code_elim_pass.cpp

@@ -306,16 +306,14 @@ void AggressiveDCEPass::ProcessDebugInformation(
         auto def = get_def_use_mgr()->GetDef(id);
         if (!live_insts_.Set(def->unique_id())) {
           AddToWorklist(inst);
+          uint32_t undef_id = Type2Undef(def->type_id());
+          inst->SetInOperand(kDebugValueValue, {undef_id});
           context()->get_def_use_mgr()->UpdateDefUse(inst);
-          worklist_.push(def);
-          def->SetOpcode(spv::Op::OpUndef);
-          def->SetInOperands({});
           id = inst->GetSingleWordInOperand(kDebugValueLocalVariable);
           auto localVar = get_def_use_mgr()->GetDef(id);
           AddToWorklist(localVar);
           context()->get_def_use_mgr()->UpdateDefUse(localVar);
           AddOperandsToWorkList(localVar);
-          context()->get_def_use_mgr()->UpdateDefUse(def);
           id = inst->GetSingleWordInOperand(kDebugValueExpression);
           auto expression = get_def_use_mgr()->GetDef(id);
           AddToWorklist(expression);

test/opt/aggressive_dead_code_elim_test.cpp

@@ -8648,6 +8648,7 @@ OpExecutionMode %main LocalSize 1 1 1
 %17 = OpString "int"
 %25 = OpString "main"
 %26 = OpString ""
+; CHECK: [[VarName:%\w+]] = OpString "some_real_obvious_name"
 %30 = OpString "some_real_obvious_name"
 %33 = OpString "__dxc_setup"
 %35 = OpString "cb000c74"
@@ -8684,6 +8685,10 @@ OpDecorate %b Binding 0
 %b = OpVariable %_ptr_UniformConstant_type_buffer_image UniformConstant
 %int_1 = OpConstant %int 1
 %int_2 = OpConstant %int 2
+; CHECK: [[undef:%\w+]] = OpUndef %int
+; ADCE will create another undef and use the new one.
+; CHECK: [[undef:%\w+]] = OpUndef %int
+%198 = OpUndef %int
 %38 = OpExtInst %void %1 DebugInfoNone
 %16 = OpExtInst %void %1 DebugExpression
 %18 = OpExtInst %void %1 DebugTypeBasic %17 %uint_32 %uint_4 %uint_0
@@ -8694,7 +8699,7 @@ OpDecorate %b Binding 0
 %27 = OpExtInst %void %1 DebugFunction %25 %21 %22 %uint_4 %uint_1 %23 %26 %uint_3 %uint_4
 %28 = OpExtInst %void %1 DebugLexicalBlock %22 %uint_4 %uint_13 %27
 %31 = OpExtInst %void %1 DebugLocalVariable %30 %20 %22 %uint_5 %uint_7 %28 %uint_4
-; CHECK: %31 = OpExtInst %void %1 DebugLocalVariable %30 %20 %22 %uint_5 %uint_7 %28 %uint_4
+; CHECK: [[var:%\w+]] = OpExtInst %void {{%\w+}} DebugLocalVariable [[VarName]] 
 %34 = OpExtInst %void %1 DebugFunction %33 %21 %22 %uint_4 %uint_1 %23 %26 %uint_3 %uint_4
 %41 = OpExtInst %void %1 DebugTypeComposite %39 %uint_0 %22 %uint_0 %uint_0 %23 %40 %38 %uint_3
 %43 = OpExtInst %void %1 DebugTypeTemplateParameter %42 %18 %38 %22 %uint_0 %uint_0
@@ -8708,13 +8713,12 @@ OpDecorate %b Binding 0
 %52 = OpExtInst %void %1 DebugFunctionDefinition %34 %main
 %304 = OpExtInst %void %1 DebugScope %28 %133
 %199 = OpExtInst %void %1 DebugLine %22 %uint_5 %uint_5 %uint_3 %uint_52
-%198 = OpUndef %int
 %245 = OpExtInst %void %1 DebugValue %31 %198 %16 %int_0
 %242 = OpExtInst %void %1 DebugValue %31 %198 %16 %int_1
 %239 = OpExtInst %void %1 DebugValue %31 %198 %16 %int_2
-; CHECK: %245 = OpExtInst %void %1 DebugValue %31 %198 %16 %int_0
-; CHECK-NOT: %242 = OpExtInst %void %1 DebugValue %31 %198 %16 %int_1
-; CHECK-NOT: %239 = OpExtInst %void %1 DebugValue %31 %198 %16 %int_2
+; CHECK: {{%\w+}} = OpExtInst %void {{%\w+}} DebugValue [[var]] [[undef]] {{%\w+}} %int_0
+; CHECK-NOT: {{%\w+}} = OpExtInst %void {{%\w+}} DebugValue
+; CHECK-NOT: {{%\w+}} = OpExtInst %void {{%\w+}} DebugValue
 %160 = OpExtInst %void %1 DebugLine %22 %uint_6 %uint_6 %uint_3 %uint_10
 %147 = OpLoad %type_buffer_image %b
 OpImageWrite %147 %uint_0 %int_0 None
@@ -8731,6 +8735,61 @@ OpFunctionEnd
                         SPV_BINARY_TO_TEXT_OPTION_FRIENDLY_NAMES);
   SinglePassRunAndMatch<AggressiveDCEPass>(before, false);
 }
+
+TEST_F(AggressiveDCETest, UndefIsOutsideFunction) {
+  const std::string spirv = R"(
+  ; CHECK: OpUndef
+  ; CHECK: OpFunction %void
+               OpCapability Shader
+               OpExtension "SPV_KHR_non_semantic_info"
+          %1 = OpExtInstImport "NonSemantic.Shader.DebugInfo.100"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint GLCompute %2 "main"
+               OpExecutionMode %2 LocalSize 1 1 1
+          %3 = OpString ""
+          %4 = OpString "int"
+          %5 = OpString "x"
+          %6 = OpString "Val.set"
+          %7 = OpString "Val"
+          %8 = OpString "this"
+       %void = OpTypeVoid
+       %uint = OpTypeInt 32 0
+    %uint_11 = OpConstant %uint 11
+     %uint_5 = OpConstant %uint 5
+   %uint_100 = OpConstant %uint 100
+         %14 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+%_ptr_Function_int = OpTypePointer Function %int
+     %uint_0 = OpConstant %uint 0
+    %uint_15 = OpConstant %uint 15
+     %uint_6 = OpConstant %uint 6
+    %uint_32 = OpConstant %uint 32
+     %uint_4 = OpConstant %uint 4
+%uint_131072 = OpConstant %uint 131072
+     %uint_1 = OpConstant %uint 1
+    %uint_10 = OpConstant %uint 10
+     %uint_8 = OpConstant %uint 8
+         %26 = OpExtInst %void %1 DebugOperation %uint_0
+         %27 = OpExtInst %void %1 DebugSource %3 %3
+         %28 = OpExtInst %void %1 DebugCompilationUnit %uint_100 %uint_5 %27 %uint_11
+         %29 = OpExtInst %void %1 DebugTypeBasic %4 %uint_32 %uint_4 %uint_131072
+         %30 = OpExtInst %void %1 DebugTypeFunction %uint_0 %void
+         %31 = OpExtInst %void %1 DebugFunction %6 %30 %27 %uint_6 %uint_10 %28 %6 %uint_0 %uint_6
+         %32 = OpExtInst %void %1 DebugTypeMember %5 %29 %27 %uint_1 %uint_8 %uint_0 %uint_32 %uint_0
+         %33 = OpExtInst %void %1 DebugTypeComposite %7 %uint_1 %27 %uint_1 %uint_8 %28 %7 %uint_32 %uint_131072 %32
+         %34 = OpExtInst %void %1 DebugLocalVariable %8 %33 %27 %uint_6 %uint_10 %31 %uint_0 %uint_1
+         %35 = OpExtInst %void %1 DebugExpression %26
+          %2 = OpFunction %void None %14
+         %36 = OpLabel
+         %37 = OpVariable %_ptr_Function_int Function
+         %38 = OpExtInst %void %1 DebugValue %34 %37 %35 %uint_0
+               OpReturn
+               OpFunctionEnd
+
+)";
+
+  SinglePassRunAndMatch<AggressiveDCEPass>(spirv, true);
+}
 }  // namespace
 }  // namespace opt
 }  // namespace spvtools