[Bug debug/45882] No debug info for vars depending on unused parameter

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45882

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-01 18:11:07 UTC ---
ENTRY_VALUE's operand is 0, because in most cases you don't want to let the
various RTL passes to see through the ENTRY_VALUE rtl, they should treat the
RTL as a black box, mostly when you want to look at the operand is either for
rtx_equal_p and similar functions, or when creating those or when the debug
info is emitted from it.  If ENTRY_VALUE's operand is e rather than 0, e.g.
various RTL passes would consider the there referenced hard register (or
memory) to be live at that point, or used, etc., but it actually isn't used.