[PATCH, RFC] Fix PR16454

[Bill Schmidt]

On Wed, 2013-06-26 at 16:14 -0500, Hal Finkel wrote:
> ----- Original Message -----
> > http://llvm.org/bugs/show_bug.cgi?id=16454 demonstrates that
> > altivec.h
> > is being included along paths where it doesn't make much sense to do
> > so.
> > This file is auto-included when compiling with -faltivec.  What I'm
> > proposing is to avoid copying the -faltivec flag when the action
> > being
> > taken is to invoke the assembler or the preprocessor.
> > 
> > I've verified that this fixes the test case in question without
> > introducing any unit-test or test-suite regressions.  I also verified
> > that preprocessing a file requiring altivec extensions (like "vector
> > float x;") with the revised Clang and then compiling the resulting
> > preprocessed file still works correctly.
> > 
> > However, I really don't know anything about how all the driver
> > machinery
> > works, so I'd appreciate some extra eyes on this before I commit.
> >  I'm
> > CC'ing a few folks that were suggested.
> > 
> > For what it's worth, the test case in question is fixed by the
> > isa<PreprocessJobAction> test.  The other test is there just because
> > it
> > makes sense to me.
> > 
> > I will add the original test from the PR as a unit test if this
> > approach
> > passes muster.
> 
> I think that this makes sense; so the job action is not available from within Frontend/CompilerInvocation.cpp where the file is actually included?

Right, at least so far as I can tell.  That code doesn't appear to be
aware whence it was called.

> 
> To confirm, if you compile something with clang that crashes, thus generating a preprocessed input file, the contents of altivec.h will no longer be copied into that file, correct?

Well, this is interesting.  I get different behavior with and without
--save-temps:

$ cat crashit.c
vector float zowie wheresmycomma;

$ $LLVM_INSTALL/bin/clang -E -maltivec crashit.c
# 1 "crashit.c"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 155 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "crashit.c" 2
vector float zowie wheresmycomma;

$ $LLVM_INSTALL/bin/clang -c -maltivec crashit.c
crashit.c:1:19: error: expected ';' after top level declarator
vector float zowie wheresmycomma;
                  ^
                  ;
1 error generated.

$ $LLVM_INSTALL/bin/clang -c -maltivec --save-temps crashit.c
In file included from <built-in>:158:
<command line>:1:10: fatal error: 'altivec.h' file not found
#include "altivec.h"
         ^
1 error generated.


I guess this is why I need a driver expert.  Can anyone explain what
code path we're going down with --save-temps that causes the different
behavior?  (BTW, --save-temps produces a crashit.i identical to the
output from the -E command.)

Thanks, Hal!

Bill

> 
>  -Hal
> 
> > 
> > Thanks,
> > Bill
> > 
> > 
> > Index: lib/Driver/Tools.cpp
> > ===================================================================
> > --- lib/Driver/Tools.cpp	(revision 184947)
> > +++ lib/Driver/Tools.cpp	(working copy)
> > @@ -2844,7 +2844,10 @@ void Clang::ConstructJob(Compilation &C, const
> > Job
> >    Args.AddLastArg(CmdArgs, options::OPT_flimit_debug_info);
> >    Args.AddLastArg(CmdArgs, options::OPT_fno_limit_debug_info);
> >    Args.AddLastArg(CmdArgs, options::OPT_fno_operator_names);
> > -  Args.AddLastArg(CmdArgs, options::OPT_faltivec);
> > +  // -faltivec causes inclusion of altivec.h, which makes no sense
> > for
> > +  // an assembly or preprocess action.
> > +  if (!isa<AssembleJobAction>(JA) && !isa<PreprocessJobAction>(JA))
> > +    Args.AddLastArg(CmdArgs, options::OPT_faltivec);
> >    Args.AddLastArg(CmdArgs,
> >    options::OPT_fdiagnostics_show_template_tree);
> >    Args.AddLastArg(CmdArgs, options::OPT_fno_elide_type);
> >  
> > 
> > 
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> > 
>