Tcl Source Code

When a unix build is configured with --disable-symbols, the NDEBUG preprocessor directive occurs twice in the compiler command. This indicates cluttered logic somewhere upstream.

This patch proposes to resolve the clutter through removal of a specific assignment of this directive in the file unix/Makefile.in.

An analysis[*] of tcl.m4 and Makefile.in (fossil trunk) led to the following:
- The preprocessor directive NDEBUG is assigned to two different variables, introducing two separate processing paths by which it propagates through the code.
- These two assignments occur relatively far apart in the code, in different files (Makefile.in and tcl.m4)
- (luckily) These two different processing paths are not (yet) intermingled. They are separately leading to a duplication in the compiler command. The reason is that the two assignments are done under the same conceptual conditions (optimization and --disable-symbols).

Other considerations:
- -DNDEBUG doesn't merit its place as a part of CFLAGS_OPTIMIZE. It's not an optimization flag for the C compiler; it's a preprocessor directive. The assignment to DEFS through AC_DEFINE() in tcl.m4 is the appropriate way.
- The still separate propagation paths leave us with a promise of a simple remedy: eliminating one of these propagations, before more clutter is being introduced on top if it.

The attached patch removes the assignment of the NDEBUG preprocessor directive from CFLAGS_OPTIMIZE (Makefile.in). This ticket is in line with patch ticket bc16203b0e.

Sincerely,

Erik Leunissen
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[*] Analysis details:

Commit history in fossil (trunk):
1. artifact [00503f3b97] introduces -DNDEBUG as an assignment to CFLAGS_OPTIMIZE in unix/Makefile.in (2009-07-18)
2. artifact [c0abbe2663] introduces -DNDEBUG as an assignment to DEFS through AC_DEFINE() in unix/tcl.m4 (2012-04-11)

1. The code path w.r.t. assignment to CFLAGS_OPTIMIZE:
- _DNDEBUG is assigned to CFLAGS_OPTIMIZE unconditionally
- CFLAGS_DEFAULT equals CFLAGS_OPTIMIZE only if ./configured with --disable-symbols (tcl.m4)
- CFLAGS_OPTIMIZE is never assigned to another variable than CFLAGS_DEFAULT (tcl.m4)
- CFLAGS_DEFAULT is never assigned to another variable than CFLAGS (Makefile.in)

2. The code path w.r.t. assignment to DEFS:
- -DNDEBUG is assigned to DEFS only if ./configured with --disable-symbols (tcl.m4)
- DEFS == AC_CFLAGS (Makefile.in)

3. The two code paths join:
The compiler commands composed by Makefile.in, use variables (like CC_SWITCHES) that are composed of both AC_FLAGS and CFLAGS, without exception. This makes that the compiler commands, if they contain -DNDEBUG, they always end up having it twice, supplied by two different code paths.

-- end of message --

Fixed in: [0a2e3bb2d9434f88]. Thanks for this report, fully agreed on this analysis!