Add second optimization for get_declaration_of, and fix some corner case bugs

On my machine, with this commit here are some typical cppfront compile time data points:
- `reflect.h2`: 0.5s
- `pure2-last-use.cpp2`: 0.3s
- all 134 regression tests: 6.3s

When I added the optimization to cache results of calls to g_d_o and checked the results to make sure they were unchanged, I noticed that in fact g_d_o was occasionally returning different answers in different calls for the same arguments. All the examples I found were corner cases in `pure2-last-use.cpp2`. The lookup bugs I found are now fixed in this commit.

This commit moves the `-_debug` command line flag from reporting stack instrumentation to reporting things I'm now coding here: Now using that flag will check the g_d_o results computed with vs. without the two new optimizations and ensure the answers are the same. (Disclaimer: Because this exercise led to a few bug fixes, which were applied to both the old and new functions, this isn't quite identical to comparing it to the true "old" way which contained a couple of I-think-innocuous-but-now-fixed bugs. The proof of the pudding is in the regression tests being identical.)

Author: hsutter

Diff for: regression-tests/test-results/run-tests.bat

@@ -3,6 +3,9 @@ cppfront.exe -version > version
 del *.cpp *.output
 copy ..\*.cpp2 .
 set count=0
+
+set STARTTIME=%TIME%
+
 for %%f in (mixed-*.cpp2) do (
     echo Starting cppfront.exe %%f
     cppfront.exe %%f > %%f.output 2>&1
@@ -29,3 +32,8 @@ echo.      %total_count% total
 if %total_count% NEQ %count% (
     echo.      *** MISMATCH: should equal total tests run
 )
+
+set ENDTIME=%TIME%
+echo.
+echo Start time: %STARTTIME%
+echo   End time: %ENDTIME%

Diff for: source/common.h

@@ -977,7 +977,7 @@ struct error_entry
 template <typename T>
 class stable_vector
 {
-    static constexpr size_t PageSize = 3; // 1'000;
+    static constexpr size_t PageSize = 1'000;
 
     std::vector< std::vector<T> > data;
 
@@ -1033,10 +1033,15 @@ class stable_vector
     }
 
     auto pop_back() -> void {
-        data.back().pop_back();
-        if (data.back().size() == 0) {
+        bounds_safety.enforce(size() > 0);
+        if (
+            data.back().empty()
+            && data.size() > 1
+            )
+        {
             data.pop_back();
         }
+        data.back().pop_back();
     }
 
     //-------------------------------------------------------------------
@@ -1190,21 +1195,21 @@ class stackinstr
 
 public:
     struct guard {
-        guard( std::string_view name, std::string_view file, int line, char* p ) {
-            if (flag_internal_debug) {
-                entries.emplace_back(name, file, line ,p);
-                if (ssize(deepest) < ssize(entries)) {
-                    deepest = entries;
-                }
-                if (largest.empty() || largest.back().cumulative < entries.back().cumulative) {
-                    largest = entries;
-                }
-            }
+        guard( std::string_view /*name*/, std::string_view /*file*/, int /*line*/, char* /*p*/ ) {
+            //if (flag_internal_debug) {
+            //    entries.emplace_back(name, file, line ,p);
+            //    if (ssize(deepest) < ssize(entries)) {
+            //        deepest = entries;
+            //    }
+            //    if (largest.empty() || largest.back().cumulative < entries.back().cumulative) {
+            //        largest = entries;
+            //    }
+            //}
         }
         ~guard() {
-            if (flag_internal_debug) {
-                entries.pop_back();
-            }
+            //if (flag_internal_debug) {
+            //    entries.pop_back();
+            //}
         }
     };
 

Diff for: source/cppfront.cpp

@@ -141,10 +141,10 @@ auto main(
         }
     }
 
-    if (flag_internal_debug) {
-        stackinstr::print_deepest();
-        stackinstr::print_largest();
-    }
+    //if (flag_internal_debug) {
+    //    stackinstr::print_deepest();
+    //    stackinstr::print_largest();
+    //}
 
     return exit_status;
 }