Re: [creduce-dev] [RFC] Adding passes for reducing clang crash reports

[John Regehr <regehr@cs.utah.edu>]

Hi Reid, that's odd, I got Amy's mail from the list as usual.

I reproduce it below.

John


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Hi all,

Reducing crashes in clang is a common task for compiler developers, so 
we would like to make it faster. Clang produces crash reports using 
“clang -E -frewrite-includes”, which leaves behind macro defines, line 
markers, ifdefs, etc. It does this because sometimes diagnostics and 
crashes in diagnostic code depend on the pre-processor state controlled 
by these directives. For example,

- Sometimes when line markers are removed, errors in system headers are 
no longer suppressed; this prevents the original crash from occurring

- Sometimes the crash depends on macros

Some of the code patterns that -frewrite-includes produces are line 
markers, #defines, and #includes contained in this type of ifelse block:

#if 0

#include "foo.h"

#else

// contents of foo.h

#endif

Currently CReduce removes the includes one by one at the beginning, and 
most of the other stuff in the lines pass, which is time consuming 
especially as they don't get collapsed by topformflat. Basically what we 
want to do is have some sort of pass to remove/simplify the line 
markers, macros, and ifs at the beginning. Maybe it could be added as an 
additional pass, or maybe as a sort of clang preprocessor step?

Any thoughts or suggestions?