Implemented a feature where the expression parser

can avoid running the code in the target if the
expression's result is known and the expression
has no side effects.

Right now this feature is quite conservative in
its guess about side effects, and it only computes
integer results, but the machinery to make it more
sophisticated is there.

llvm-svn: 121952

1 files changed, 47 insertions, 32 deletions

diff --git a/lldb/source/Expression/ClangUserExpression.cpp b/lldb/source/Expression/ClangUserExpression.cpp
index 278cee773c1..0085c8a9bb8 100644
--- a/lldb/source/Expression/ClangUserExpression.cpp
+++ b/lldb/source/Expression/ClangUserExpression.cpp
@@ -22,10 +22,11 @@
 #include "lldb/Core/Log.h"
 #include "lldb/Core/StreamString.h"
 #include "lldb/Core/ValueObjectConstResult.h"
+#include "lldb/Expression/ASTSplitConsumer.h"
+#include "lldb/Expression/ASTResultSynthesizer.h"
 #include "lldb/Expression/ClangExpressionDeclMap.h"
 #include "lldb/Expression/ClangExpressionParser.h"
 #include "lldb/Expression/ClangFunction.h"
-#include "lldb/Expression/ASTResultSynthesizer.h"
 #include "lldb/Expression/ClangUserExpression.h"
 #include "lldb/Host/Host.h"
 #include "lldb/Symbol/VariableList.h"
@@ -143,7 +144,8 @@ ApplyUnicharHack(std::string &expr)
 bool
 ClangUserExpression::Parse (Stream &error_stream, 
                             ExecutionContext &exe_ctx,
-                            TypeFromUser desired_type)
+                            TypeFromUser desired_type,
+                            lldb::ClangExpressionVariableSP *const_result)
 {
     lldb::LogSP log(lldb_private::GetLogIfAllCategoriesSet (LIBLLDB_LOG_EXPRESSIONS));
     
@@ -292,8 +294,8 @@ ClangUserExpression::Parse (Stream &error_stream,
     m_dwarf_opcodes.reset();
     
     lldb::addr_t jit_end;
-    
-    Error jit_error = parser.MakeJIT (m_jit_addr, jit_end, exe_ctx);
+        
+    Error jit_error = parser.MakeJIT (m_jit_addr, jit_end, exe_ctx, const_result);
     
     m_expr_decl_map->DidParse();
     
@@ -601,10 +603,12 @@ ClangUserExpression::Evaluate (ExecutionContext &exe_ctx,
 
     StreamString error_stream;
     
+    lldb::ClangExpressionVariableSP const_result;
+    
     if (log)
         log->Printf("== [ClangUserExpression::Evaluate] Parsing expression %s ==", expr_cstr);
     
-    if (!user_expression_sp->Parse (error_stream, exe_ctx, TypeFromUser(NULL, NULL)))
+    if (!user_expression_sp->Parse (error_stream, exe_ctx, TypeFromUser(NULL, NULL), &const_result))
     {
         if (error_stream.GetString().empty())
             error.SetErrorString ("expression failed to parse, unknown error");
@@ -615,41 +619,52 @@ ClangUserExpression::Evaluate (ExecutionContext &exe_ctx,
     {
         lldb::ClangExpressionVariableSP expr_result;
 
-        error_stream.GetString().clear();
-        
-        if (log)
-            log->Printf("== [ClangUserExpression::Evaluate] Executing expression ==");
-
-        execution_results = user_expression_sp->Execute (error_stream, 
-                                                         exe_ctx, 
-                                                         discard_on_error, 
-                                                         user_expression_sp, 
-                                                         expr_result);
-        if (execution_results != lldb::eExecutionCompleted)
+        if (const_result.get())
         {
             if (log)
-                log->Printf("== [ClangUserExpression::Evaluate] Execution completed abnormally ==");
+                log->Printf("== [ClangUserExpression::Evaluate] Expression evaluated as a constant ==");
             
-            if (error_stream.GetString().empty())
-                error.SetErrorString ("expression failed to execute, unknown error");
-            else
-                error.SetErrorString (error_stream.GetString().c_str());
+            result_valobj_sp = const_result->GetValueObject();
         }
-        else 
-        {
-            if (expr_result)
+        else
+        {    
+            error_stream.GetString().clear();
+            
+            if (log)
+                log->Printf("== [ClangUserExpression::Evaluate] Executing expression ==");
+
+            execution_results = user_expression_sp->Execute (error_stream, 
+                                                             exe_ctx, 
+                                                             discard_on_error, 
+                                                             user_expression_sp, 
+                                                             expr_result);
+            
+            if (execution_results != lldb::eExecutionCompleted)
             {
-                result_valobj_sp = expr_result->GetValueObject();
-                
                 if (log)
-                    log->Printf("== [ClangUserExpression::Evaluate] Execution completed normally with result %s ==", result_valobj_sp->GetValueAsCString(exe_ctx.GetBestExecutionContextScope()));
+                    log->Printf("== [ClangUserExpression::Evaluate] Execution completed abnormally ==");
+                
+                if (error_stream.GetString().empty())
+                    error.SetErrorString ("expression failed to execute, unknown error");
+                else
+                    error.SetErrorString (error_stream.GetString().c_str());
             }
-            else
+            else 
             {
-                if (log)
-                    log->Printf("== [ClangUserExpression::Evaluate] Execution completed normally with no result ==");
-                
-                error.SetErrorString ("Expression did not return a result");
+                if (expr_result)
+                {
+                    result_valobj_sp = expr_result->GetValueObject();
+                    
+                    if (log)
+                        log->Printf("== [ClangUserExpression::Evaluate] Execution completed normally with result %s ==", result_valobj_sp->GetValueAsCString(exe_ctx.GetBestExecutionContextScope()));
+                }
+                else
+                {
+                    if (log)
+                        log->Printf("== [ClangUserExpression::Evaluate] Execution completed normally with no result ==");
+                    
+                    error.SetErrorString ("Expression did not return a result");
+                }
             }
         }
     }