On Thu, May 3, 2012 at 3:30 PM, Matt Davis <mattdav...@gmail.com> wrote: > I have been fighting with a simple problem for the past few nights. In my > GIMPLE pass I create a variable, an ssa name for that variable, and then > assign > it to the LHS of a call I build: > > call = gimple_build_call(fndecl, 0); > decl = create_tmp_var(TREE_TYPE(TREE_TYPE(test_decode_fndecl)), "FOO"); > ssa = make_ssa_name(decl, call); > gimple_set_lhs(call, ssa); > gsi_insert_before(&gsi, call, GSI_SAME_STMT); > > I verify the GIMPLE and it looks proper: > > char * FOO.2; > /* some gimple code */ > FOO.2_8 = fn(); > strcat(&mylocal, FOO.2_8);
Probably for the use stmt you did not call update_stmt. You can check in the debugger by debug_immediate_uses () which likely prints no use for FOO.2_8 > > However, when I build with -Os the GIMPLE looks like: > char * FOO.2; > /* some gimple code */ > fn(); > strcat(&mylocal, FOO.2_8); > > And the compiler segfaults in "ptr_deref_may_alias_decl_p" for 'ptr' FOO.2_8 > and > 'decl' mylocal arguments. The segfault occurs because TREE_TYPE(ptr) is NULL > and calling POINTER_TYPE_P(TREE_TYPE(ptr)) dereferences a NULL. That's what happens when an SSA name is released. > After more debugging, it is eliminate_unnecessary_stmts() which tries to > remove > the 'FOO.2_8 = fn();' statement. In that routine, the LHS is considered > "dead" > and because of that the routine sets the LHS to NULL. It's dead if it has no uses. > So, I guess my question is, how can I force this stmt to hang around? I > looked > at eliminate_unnecessary_stmts, and do not see any specific flags I can set to > the stmt to make 'em hang around, and I do not know what to do to make LHS > appear not "dead." Even if I set 'ssa' TREE_USED and 'decl' as > DECL_PRESERVE_P. Well, that's not how SSA uses/defs work. > Thanks for any information! > > -Matt
