Build configuration

The box to the left of the toolbar’s build buttons chooses the architecture that the project is compiled for, and starts the compiler in safe mode. It is the only build setting that is a choice of the IDE and not a setting of the project.

The box is a drop-down list with three entries, and its tooltip is Choose a build configuration.

win32: Compiles a 32-bit program.
win64: Compiles a 64-bit program. See Project Types for a DLL called from VBA or Excel.
safeMode: Opens the project without the compiler. See Safe mode.

There are no Debug and Release entries, and none for AnyCPU or ARM. The split between the program that runs in the IDE and the program that a build writes is made in Project Settings, by two sets of options: Compiler Options (BUILD) for Build and Compiler Options (DEBUG) for Start.

Changing the architecture

Ctrl+F1 chooses win64 and Ctrl+F2 chooses win32. They do nothing when the box already shows the entry. Manage Keyboard Shortcuts can change them.

A change restarts the compiler as a program of the other architecture. The IDE does not ask first. A program that is running or paused is ended at once. While the new compiler loads the project, a box that says Please wait… covers the IDE, for about ten seconds in a small project. Then:

the CALL STACK, VARIABLES, WATCHES and HISTORY panels and the list of running programs are empty;
the DIAGNOSTICS rows are cleared;
every open form designer shows the RESYNC treatment, as it does after any restart of the compiler.

With no project open, nothing restarts: the box only sets what the next project will use.

What the choice changes

The file. A win32 build writes a 32-bit file and a win64 build a 64-bit one. ${Architecture} in the Build Output Path is win32 or win64, and ${Bitness} is 32 or 64. The default path puts ${Architecture} in the file name, so the two builds sit side by side.
The code. #If Win64 is true in win64 and false in win32, and LongPtr is 8 bytes in win64. The editor treats a branch of an #If Win64 block as active or greys it out to match. Compiler Constants shows the same code in both modes.
The program that runs in the IDE. Start (F5) and Run Or Preview (F6) run the project in the compiler process, so a win64 run is a 64-bit program. See Running.

Two other settings of the project decide which compiler program runs it: Large Address Aware (LAA) and Data Execution Prevention Aware (DEP). When the project’s settings do not match the compiler that is running, the IDE starts a compiler that does, and loads the project in it. The built file follows the same two settings.

Where the choice is kept

The IDE keeps the choice for each project, under the path of its .twinproj file, in its own settings (the targetArchitectureMemory value; see where the IDE keeps its settings). It is not in the project: the Settings file does not hold it, and a copy of the project on another machine starts with the box as that machine’s IDE shows it.

When you open a project from its file, from Open Recent or from the command line, the IDE sets the box to the remembered choice before the project loads. A project with no remembered choice leaves the box as it is. A project made from a template, a sample or a folder reads no choice, and a project imported from a VB6 project starts as win32. A project that was never saved has no path, so its choice lasts for the session.

Safe mode

safeMode opens the project’s files without starting the compiler’s services. It gives access to the project’s files when the compiler’s services get in the way, for example when the compiler keeps crashing. After a project loads in safe mode, a box explains it, in these words: SafeMode is designed to give you access to the file system of your project, without starting all of the associated compiler services. Use this mode to investigate / fix / recover your code before saving and restarting in normal mode. Choose OK.

In safe mode:

Build and Clean look available and do nothing. No line is written and no box opens.
The DIAGNOSTICS rows are not cleared, and the form designer’s RESYNC button answers Can’t resync the form designer in Safe Mode.
The choice is not remembered, and no remembered choice is read when a project opens.

The IDE switches to safe mode on its own when it has restarted the compiler more than three times in 60 seconds. It says Compiler crash loop detected. Restarting in SAFE mode.

Restart the compiler

The toolbar button Restart the compiler and Tools → Restart the compiler end the compiler and start a new one, for the architecture the box shows. With Alt held, the button also restarts the process that caches LLVM code. Running describes what a restart does to a running program.