Keep DebugBuildIdentifier during dce (KhronosGroup#6166)

It is expected that no other instructions should refer to the
DebugBuildIdentifier instruction, but this causes it to be removed
during dead code elimination. Instead keep the instruction if it is
found.

Author: jarcherNV

source/opt/aggressive_dead_code_elim_pass.cpp

@@ -914,6 +914,10 @@ bool AggressiveDCEPass::ProcessGlobalValues() {
       context()->AnalyzeUses(&dbg);
       continue;
     }
+    // Save debug build identifier even if no other instructions refer to it.
+    if (dbg.GetShader100DebugOpcode() ==
+        NonSemanticShaderDebugInfo100DebugBuildIdentifier)
+      continue;
     to_kill_.push_back(&dbg);
     modified = true;
   }

test/opt/optimizer_test.cpp

@@ -506,6 +506,72 @@ OpFunctionEnd)";
   EXPECT_EQ(test_disassembly, default_disassembly);
 }
 
+TEST(Optimizer, KeepDebugBuildIdentifierAfterDCE) {
+  // Test that DebugBuildIdentifier is not removed after DCE.
+  const std::string before = R"(
+OpCapability Shader
+OpExtension "SPV_KHR_non_semantic_info"
+%1 = OpExtInstImport "NonSemantic.Shader.DebugInfo.100"
+OpMemoryModel Logical GLSL450
+OpEntryPoint GLCompute %main "main"
+OpExecutionMode %main LocalSize 8 8 1
+%4 = OpString "8937d8f571cf7b58d86d9d66196024f5d04e3186"
+%7 = OpString ""
+%9 = OpString ""
+OpSource Slang 1
+%19 = OpString ""
+%24 = OpString ""
+%25 = OpString ""
+OpName %main "main"
+%void = OpTypeVoid
+%uint = OpTypeInt 32 0
+%uint_0 = OpConstant %uint 0
+%uint_11 = OpConstant %uint 11
+%uint_5 = OpConstant %uint 5
+%uint_100 = OpConstant %uint 100
+%15 = OpTypeFunction %void
+%uint_6 = OpConstant %uint 6
+%uint_7 = OpConstant %uint 7
+%uint_1 = OpConstant %uint 1
+%uint_2 = OpConstant %uint 2
+%3 = OpExtInst %void %1 DebugBuildIdentifier %4 %uint_0
+%8 = OpExtInst %void %1 DebugSource %9 %7
+%13 = OpExtInst %void %1 DebugCompilationUnit %uint_100 %uint_5 %8 %uint_11
+%17 = OpExtInst %void %1 DebugTypeFunction %uint_0 %void
+%18 = OpExtInst %void %1 DebugFunction %19 %17 %8 %uint_5 %uint_6 %13 %19 %uint_0 %uint_5
+%23 = OpExtInst %void %1 DebugEntryPoint %18 %13 %24 %25
+%main = OpFunction %void None %15
+%16 = OpLabel
+%21 = OpExtInst %void %1 DebugFunctionDefinition %18 %main
+%32 = OpExtInst %void %1 DebugScope %18
+%26 = OpExtInst %void %1 DebugLine %8 %uint_7 %uint_7 %uint_1 %uint_2
+OpReturn
+%33 = OpExtInst %void %1 DebugNoScope
+OpFunctionEnd
+  )";
+
+  std::vector<uint32_t> binary;
+  SpirvTools tools(SPV_ENV_VULKAN_1_3);
+  tools.Assemble(before, &binary,
+                 SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
+
+  Optimizer opt(SPV_ENV_VULKAN_1_3);
+  opt.RegisterPerformancePasses().RegisterPass(CreateAggressiveDCEPass());
+
+  std::vector<uint32_t> optimized;
+  ASSERT_TRUE(opt.Run(binary.data(), binary.size(), &optimized))
+      << before << "\n";
+
+  std::string after;
+  tools.Disassemble(optimized.data(), optimized.size(), &after,
+                    SPV_BINARY_TO_TEXT_OPTION_NO_HEADER);
+
+  // Test that the DebugBuildIdentifier is not removed after DCE.
+  bool found = after.find("DebugBuildIdentifier") != std::string::npos;
+  EXPECT_TRUE(found)
+      << "Was expecting the DebugBuildIdentifier to have been kept.";
+}
+
 }  // namespace
 }  // namespace opt
 }  // namespace spvtools