spirv-opt: fix crash in function declarations (#5796)

* spirv-opt: fix crash in function declarations

Function declarations contain no blocks, so bail before segfaulting
in function optimization passes that operate on blocks.

Fixes #5795

* spirv-opt: add test for optimizing declarations

Author: cheneym2

source/opt/aggressive_dead_code_elim_pass.cpp

@@ -267,6 +267,7 @@ void AggressiveDCEPass::AddBreaksAndContinuesToWorklist(
 }
 
 bool AggressiveDCEPass::AggressiveDCE(Function* func) {
+  if (func->IsDeclaration()) return false;
   std::list<BasicBlock*> structured_order;
   cfg()->ComputeStructuredOrder(func, &*func->begin(), &structured_order);
   live_local_vars_.clear();

source/opt/mem_pass.cpp

@@ -415,6 +415,7 @@ void MemPass::RemoveBlock(Function::iterator* bi) {
 }
 
 bool MemPass::RemoveUnreachableBlocks(Function* func) {
+  if (func->IsDeclaration()) return false;
   bool modified = false;
 
   // Mark reachable all blocks reachable from the function's entry block.

test/opt/aggressive_dead_code_elim_test.cpp

@@ -8070,6 +8070,42 @@ TEST_F(AggressiveDCETest, StoringAPointer) {
   SinglePassRunAndMatch<AggressiveDCEPass>(text, true);
 }
 
+TEST_F(AggressiveDCETest, FunctionDeclaration) {
+  // Ensure the optimizer can handle traversing over a function declaration
+  // 'myfunc' which has no blocks
+
+  const std::string text = R"(OpCapability Linkage
+OpCapability Shader
+OpMemoryModel Logical GLSL450
+OpEntryPoint Fragment %PSMain "main" %entryPointParam_PSMain
+OpExecutionMode %PSMain OriginUpperLeft
+OpSource Slang 1
+OpName %myfunc "myfunc"
+OpName %entryPointParam_PSMain "entryPointParam_PSMain"
+OpName %PSMain "PSMain"
+OpDecorate %myfunc LinkageAttributes "_S6myfuncp0pv4f" Import
+OpDecorate %entryPointParam_PSMain Location 0
+%void = OpTypeVoid
+%5 = OpTypeFunction %void
+%float = OpTypeFloat 32
+%v4float = OpTypeVector %float 4
+%8 = OpTypeFunction %v4float
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+%entryPointParam_PSMain = OpVariable %_ptr_Output_v4float Output
+%myfunc = OpFunction %v4float None %8
+OpFunctionEnd
+%PSMain = OpFunction %void None %5
+%10 = OpLabel
+%11 = OpFunctionCall %v4float %myfunc
+OpStore %entryPointParam_PSMain %11
+OpReturn
+OpFunctionEnd
+)";
+
+  SetAssembleOptions(SPV_TEXT_TO_BINARY_OPTION_PRESERVE_NUMERIC_IDS);
+  SinglePassRunAndCheck<AggressiveDCEPass>(text, text, true, true);
+}
+
 }  // namespace
 }  // namespace opt
 }  // namespace spvtools