Index: lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp
+++ lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp
@@ -9,6 +9,7 @@
#include "ASTResultSynthesizer.h"
#include "ClangASTImporter.h"
+#include "ClangExpressionSourceCode.h"
#include "ClangPersistentVariables.h"
#include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
@@ -209,6 +210,14 @@
return false;
Stmt **last_stmt_ptr = Body->body_end() - 1;
+ // The last statement in the expression is our injected call to
+ // __lldb_use_expr_result. The expression before is the actual user expression
+ // so skip the injected function call.
+ CallExpr *use_call = cast<CallExpr>(*last_stmt_ptr);
+ assert(cast<FunctionDecl>(use_call->getCalleeDecl())->getName() ==
+ ClangExpressionSourceCode::GetUseExprResultFunctionName());
+ --last_stmt_ptr;
+
Stmt *last_stmt = *last_stmt_ptr;
while (dyn_cast<NullStmt>(last_stmt)) {
@@ -380,6 +389,52 @@
*last_stmt_ptr = static_cast<Stmt *>(result_initialization_stmt_result.get());
+ // At this point we created the result variable that stores the result of
+ // the last expression. However, in a situation where we finish on a local
+ // variable, the expression result is just a pointer to something on the stack
+ // and LLVM will optimize that away. E.g., `MyClass c; c` becomes:
+ //
+ // MyClass c;
+ // static MyClass *__lldb_expr_result_ptr = &c; // Points to stack.
+ // } // End of expression function.
+ //
+ // The optimizer will just remove this store. So we add a trailing call to
+ // the undefined function `__lldb_use_expr_result` which will take an address
+ // of `__lldb_expr_result_ptr`. We will manually remove that call later,
+ // but until we remove that function the optimizer can no longer remove
+ // the store to our result variable:
+ //
+ // MyClass c;
+ // static MyClass *__lldb_expr_result_ptr = &c; // Points to stack.
+ // __lldb_expr_result_ptr(__lldb_expr_result_ptr);
+ // } // End of expression function.
+ //
+ // We already have a call at the end in the form:
+ // __lldb_expr_result_ptr(nullptr);
+ // which we injected into the wrapping source code. We just need to change
+ // the placeholder `nullptr` argument to the result variable we created above
+ // and do any casting.
+ Expr *ref_result = DeclRefExpr::Create(
+ Ctx, NestedNameSpecifierLoc(), SourceLocation(), result_decl,
+ /*RefersToEnclosingVariableOrCapture=*/false, SourceLocation(),
+ result_decl->getType(), ExprValueKind::VK_LValue);
+ QualType ref_type = ref_result->getType();
+ // __lldb_expr_result isn't a pointer for non-lvalues, so inject an &:
+ // __lldb_expr_result_ptr(&__lldb_expression_result)
+ if (!ref_type->isPointerType())
+ ref_result = UnaryOperator::Create(
+ Ctx, ref_result, UnaryOperator::Opcode::UO_AddrOf,
+ Ctx.getPointerType(ref_type), ExprValueKind::VK_RValue,
+ ExprObjectKind::OK_Ordinary, SourceLocation(), /*CanOverflow=*/false,
+ FPOptionsOverride());
+ // Cast the pointer type we have to void so that the type system is not
+ // complaining.
+ ImplicitCastExpr *c = ImplicitCastExpr::Create(
+ Ctx, Ctx.VoidPtrTy, CastKind::CK_BitCast, ref_result, nullptr,
+ ExprValueKind::VK_RValue, FPOptionsOverride());
+ // Overwrite the placeholder argument.
+ use_call->getArgs()[0] = c;
+
return true;
}
Index: lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp
+++ lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp
@@ -44,11 +44,13 @@
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
+#include "llvm/Passes/PassBuilder.h"
#include "llvm/Support/DynamicLibrary.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Host.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Signals.h"
+#include "llvm/Transforms/IPO/PassManagerBuilder.h"
#include "ClangDiagnostic.h"
#include "ClangExpressionParser.h"
@@ -648,8 +650,18 @@
CodeGenOptions::FramePointerKind::All);
if (generate_debug_info)
m_compiler->getCodeGenOpts().setDebugInfo(codegenoptions::FullDebugInfo);
- else
+ else {
m_compiler->getCodeGenOpts().setDebugInfo(codegenoptions::NoDebugInfo);
+ // If the user doesn't want to debug the expression we can optimize it.
+ // This makes it run a bit faster in case it's a long-running expression
+ // and it makes the life of the IRInterpreter easier as all the verbose
+ // IR nodes generated by Clang are simplified.
+ // The level set here gets propagated to the pass manager.
+ m_compiler->getCodeGenOpts().OptimizationLevel = 2;
+ // LLVM's lifetime markers aren't supported by the IRInterpreter so avoid
+ // generating them.
+ m_compiler->getCodeGenOpts().DisableLifetimeMarkers = true;
+ }
// Disable some warnings.
SetupDefaultClangDiagnostics(*m_compiler);
@@ -1319,6 +1331,45 @@
return false;
}
+static void RunOptimizationPipeline(llvm::Module &module,
+ clang::CodeGenOptions &opts) {
+ // Build a fitting target machine for our triple.
+ llvm::Triple triple(module.getTargetTriple());
+ std::unique_ptr<llvm::TargetMachine> target_machine;
+ llvm::SmallVector<std::string, 0> mAttrs;
+ target_machine.reset(llvm::EngineBuilder().selectTarget(triple,
+ /*MArch=*/"",
+ /*MCPU=*/"", mAttrs));
+
+ // Build the default analysis managers.
+ LoopAnalysisManager LAM;
+ FunctionAnalysisManager FAM;
+ CGSCCAnalysisManager CGAM;
+ ModuleAnalysisManager MAM;
+
+ PassInstrumentationCallbacks PIC;
+ Optional<PGOOptions> P;
+ PipelineTuningOptions PTO;
+ PassBuilder PB(target_machine.get(), PTO, P, &PIC);
+
+ // Register all passes.
+ PB.registerModuleAnalyses(MAM);
+ PB.registerCGSCCAnalyses(CGAM);
+ PB.registerFunctionAnalyses(FAM);
+ PB.registerLoopAnalyses(LAM);
+ PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
+
+ ModulePassManager MPM;
+ // Pick a pipeline that fits to our CodeGenOpts optimization level and add
+ // the respective passes.
+ std::string pipelineString =
+ "default<O" + std::to_string(opts.OptimizationLevel) + ">";
+ if (auto Err = PB.parsePassPipeline(MPM, pipelineString))
+ llvm_unreachable("Failed to parse pipeline");
+
+ MPM.run(module, MAM);
+}
+
lldb_private::Status ClangExpressionParser::PrepareForExecution(
lldb::addr_t &func_addr, lldb::addr_t &func_end,
lldb::IRExecutionUnitSP &execution_unit_sp, ExecutionContext &exe_ctx,
@@ -1407,6 +1458,17 @@
return err;
}
+ // Run the default LLVM optimization passes over the generated module unless
+ // this is an expression that the user wants to debug (in which case the
+ // optimizations would degrade the debug experience).
+ if (!GetGenerateDebugInfo())
+ RunOptimizationPipeline(*execution_unit_sp->GetModule(),
+ m_compiler->getCodeGenOpts());
+ // Remove the injected function call that prevents the optimizer from
+ // removing the seemingly dead store of the expression result.
+ ir_for_target.RemoveAllCallsToFunction(
+ ClangExpressionSourceCode::GetUseExprResultFunctionName());
+
Process *process = exe_ctx.GetProcessPtr();
if (execution_policy != eExecutionPolicyAlways &&
Index: lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.h
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.h
+++ lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.h
@@ -73,6 +73,10 @@
bool GetOriginalBodyBounds(std::string transformed_text,
size_t &start_loc, size_t &end_loc);
+ /// Returns the name of the function that is injected in the source code
+ /// to make sure the expression result is considered used by the optimizer.
+ static llvm::StringRef GetUseExprResultFunctionName();
+
protected:
ClangExpressionSourceCode(llvm::StringRef filename, llvm::StringRef name,
llvm::StringRef prefix, llvm::StringRef body,
Index: lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
+++ lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp
@@ -32,6 +32,8 @@
#define PREFIX_NAME "<lldb wrapper prefix>"
#define SUFFIX_NAME "<lldb wrapper suffix>"
+/// \see ClangExpressionSourceCode::GetUseExprResultFunctionName
+#define LLDB_USE_EXPR_RESULT "__lldb_use_expr_result"
const llvm::StringRef ClangExpressionSourceCode::g_prefix_file_name = PREFIX_NAME;
@@ -71,6 +73,7 @@
extern "C"
{
int printf(const char * __restrict, ...);
+ void )" LLDB_USE_EXPR_RESULT R"((void *);
}
)";
@@ -415,6 +418,7 @@
"{ \n"
" %s; \n"
"%s"
+ " " LLDB_USE_EXPR_RESULT "(0);\n"
"} \n",
module_imports.c_str(), m_name.c_str(),
lldb_local_var_decls.GetData(), tagged_body.c_str());
@@ -427,6 +431,7 @@
"{ \n"
" %s; \n"
"%s"
+ " " LLDB_USE_EXPR_RESULT "(nullptr); \n"
"} \n",
module_imports.c_str(), m_name.c_str(),
lldb_local_var_decls.GetData(), tagged_body.c_str());
@@ -442,6 +447,7 @@
"{ \n"
" %s; \n"
"%s"
+ " " LLDB_USE_EXPR_RESULT "(0); \n"
"} \n"
"@end \n",
module_imports.c_str(), m_name.c_str(), m_name.c_str(),
@@ -459,6 +465,7 @@
"{ \n"
" %s; \n"
"%s"
+ " " LLDB_USE_EXPR_RESULT "(0); \n"
"} \n"
"@end \n",
module_imports.c_str(), m_name.c_str(), m_name.c_str(),
@@ -483,3 +490,7 @@
end_loc = transformed_text.find(m_end_marker);
return end_loc != std::string::npos;
}
+
+llvm::StringRef ClangExpressionSourceCode::GetUseExprResultFunctionName() {
+ return LLDB_USE_EXPR_RESULT;
+}
Index: lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.h
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.h
+++ lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.h
@@ -103,6 +103,11 @@
/// True on success; false otherwise
bool runOnModule(llvm::Module &llvm_module) override;
+ /// Removes all calls to the function with the given name in the module.
+ ///
+ /// All calls found by this function must be safe to remove.
+ void RemoveAllCallsToFunction(llvm::StringRef function_name);
+
/// Interface stub
///
/// Implementation of the llvm::ModulePass::assignPassManager() function.
Index: lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp
+++ lldb/source/Plugins/ExpressionParser/Clang/IRForTarget.cpp
@@ -364,7 +364,9 @@
LLDB_LOG(log, "Replacing \"{0}\" with \"{1}\"", PrintValue(result_global),
PrintValue(new_result_global));
- if (result_global->use_empty()) {
+ // If the old global had an initializer, create a store that initializes
+ // the new global with the same value.
+ if (result_global->hasInitializer()) {
// We need to synthesize a store for this variable, because otherwise
// there's nothing to put into its equivalent persistent variable.
@@ -374,16 +376,6 @@
if (!first_entry_instruction)
return false;
- if (!result_global->hasInitializer()) {
- LLDB_LOG(log, "Couldn't find initializer for unused variable");
-
- m_error_stream.Format("Internal error [IRForTarget]: Result variable "
- "({0}) has no writes and no initializer\n",
- result_name);
-
- return false;
- }
-
Constant *initializer = result_global->getInitializer();
StoreInst *synthesized_store =
@@ -391,9 +383,9 @@
LLDB_LOG(log, "Synthesized result store \"{0}\"\n",
PrintValue(synthesized_store));
- } else {
- result_global->replaceAllUsesWith(new_result_global);
}
+ // About to remove the old result global, so RAUW the new global.
+ result_global->replaceAllUsesWith(new_result_global);
if (!m_decl_map->AddPersistentVariable(
result_decl, m_result_name, m_result_type, true, m_result_is_pointer))
@@ -2023,6 +2015,24 @@
return true;
}
+void IRForTarget::RemoveAllCallsToFunction(llvm::StringRef function_name) {
+ for (llvm::Function &function : *m_module) {
+ for (BasicBlock &bb : function) {
+ for (BasicBlock::iterator i = bb.begin(), end = bb.end(); i != end;) {
+ if (CallInst *call = dyn_cast<CallInst>(&(*i))) {
+ if (llvm::Function *func = call->getCalledFunction()) {
+ if (func->getName() == function_name) {
+ i = call->eraseFromParent();
+ continue;
+ }
+ }
+ }
+ ++i;
+ }
+ }
+ }
+}
+
void IRForTarget::assignPassManager(PMStack &pass_mgr_stack,
PassManagerType pass_mgr_type) {}