Unspecified behaviour in java/gjavah.c

Mon Nov 25 06:16:00 GMT 2002

Diego Novillo writes:
 > After the latest merge from basic-improvements to tree-ssa, I
 > started getting failures building libjava:
 > 
 > 
 > Below is a minimal test case that exhibits the same problem:
 > 
 > -----------------------------------------------------------------------------
 > struct JCF {
 > char *read_ptr;
 > } *jcf;
 > 
 > foo()
 > {
 > jcf->read_ptr += (jcf->read_ptr += 4, 5);
 > }
 > -----------------------------------------------------------------------------
Ah. Nasty.
This is such a common problem when programming in C that I wonder if
we could include code in gcc to detect it.
When we gimplify, could we easily detect the same lvalue being updated
more than once between sequence points?
 > 	* java/jcf-reader.c: Don't expand JCF_readu4 inside the
 > 	expansion of JCF_SKIP.
OK.
Thanks for finding this.
Andrew.