Re: gcc forgets to decrease esp after function call

[Andrew Haley <aph at redhat dot com>]

Vladimir Simonov writes:
 > Andrew Haley wrote:
 > > Vladimir Simonov writes:
 > >  > The attached test case can be built by compile.sh.
 > >  > It produces two binaries - test_bin_bad & test_bin_good.
 > >  > 
 > >  > test_bin_good prints "Hello word" before exit.
 > >  > test_bin_bad crashes.
 > >  > 
 > >  > The difference is the only -O2 used while test_bin_bad build.
 > >  > 
 > >  > The symptoms are the same - incorrect esp usage in caller
 > >  > after call function returning object.
 > >  > 
 > >  > We reproduced the bug in gcc 4.1.0/4.1.1/4.1.2
 > >  > gcc 3.x can't compile the sources.
 > > 
 > > OK, we're getting closer. 
 > 
 > Hi
 > 
 > Are you capable to reproduce the bug?

Yes.

 > > Unfortunately, your test case includes a
 > > ton of system headers for one particular system/version of gcc, 
 > But it doesn't contain any #include directive.
 > It is self consistent.
 > 
 > Do you mean that I should
 > add "#include" for system headers?

Yes.  Otherwise it's not possible to compile it with any other version
of gcc than the one you built it on.  A test case should be
standalone and not depend on a particulat gcc version.

 > I think this way we may made the bug less obvious.

 > > and it
 > > also includes a lot of library code not used in your test case.
 > 
 > I understood it from the start of discussion :)
 > I hoped:

 > 1. GCC delelopers have some tools or methods to automatically
 > remove text which does not affect codegeneration. Or some compile
 > stage which contans intermediate data without unused by
 > codegeneration prototypes, classes, etc.

 > 2. GCC developers are smart enough to localize and try to fix gcc
 > having such obvious indication as this - codegenerator "forgets"
 > that it called function returning object. Is it impossible to find
 > thin place/places taking into account above, fix it and check by
 > our test?

It's up to you, really.  The more self-contained a test case you
provide, the more likely someone is to fix your problem.  Remember
that they are, in this case, volunteers, and not highly motivated to
spend a lot of time to try to remove all the extraneous code.

 > In such a case the test size has no defference in my opinion.
 > 
 > 
 > > Fillet that, and you will have a test case that can be submitted.
 > 
 > It requires a lot of mannual work - remove a peace of code, then
 > check that the test can be built, the check that the bug did not
 > disappear, etc.

It's your code, so presumably you are familiar with it.  I stepped
though the code in gdb, and it seemed that not many routines were
actually involved.

Andrew.