[PATCH, RFC] Fix PR16454

[Bill Schmidt]

On Wed, 2013-06-26 at 16:54 -0500, Bill Schmidt wrote:
> 
> 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.)

So, the patch is not acceptable as is; it introduces an error with
--save-temps even for correct code:

$ cat ok.c
vector float zowie, wheresmycomma;
$ $LLVM_INSTALL/bin/clang -c -maltivec ok.c
$ $LLVM_INSTALL/bin/clang -c -maltivec --save-temps ok.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 am not certain how to proceed.  Suggestions from driver experts
welcome.

Thanks,
Bill

> 
> 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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> > > 
> >