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Re: Latest GCC can't compile keymap.c correctly.

From: Richard Stallman
Subject: Re: Latest GCC can't compile keymap.c correctly.
Date: Thu, 07 Sep 2006 17:14:24 -0400

    When we compile only keymap.c with gcc-4.0.3 and link it,
    the problem disappears.

Either keymap.c has a bug or the latest GCC has a bug.
We need to find out which function the problem is in.

I suggest you split keymap.c into two files, and try compiling one
with each GCC version.  By moving functions between the two files you
can determine where the problem is.  (If you are using a high
optimization level that does interprocedural optimization, you may
need more subtle techniques to determine which function.)

Once you know which function it is, make a .s file with each GCC
version, and compare the two with each other and with the source code.
This way you will find where the GCC 4.2 assenbly code is wrong.  Then
you can see whether there is something in the source code that has
unspecified or undefined behavior.  If so, we should fix that.  If
not, then it is a GCC bug, and you will have all the info needed to
report it properly.

I know this is a substantial amount of work, but it is the only way
to solve the problem.  And if this is a GCC bug, it is very important
to fix it.

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