When a register is set outside of a loop and referenced inside,
update_life_info can't figure out that the set is dead because
the loop appears to still use the register according to the
lifeness information which is propagated circularily around the
loop.
delete_trivially_dead_insns can detect that such sets are dead,
and thus remove them. However, it does not update the liveness
information. This leads to a checking ICE when doing the next
global update.
The gcc 3.2 version of this patch (short version) for this problem
looks like this:
2004-05-17 J"orn Rennecke <[EMAIL PROTECTED]>
* cse.c (basic-block.h): #include.
(trivially_dead_nonlocal_regs): New variable.
(note_dead_set): New function.
(delete_trivially_dead_insns): If life info is available, update it.
The patch in its current form is conceptually dependent on the patch for
gcc/18992 being applied first and also has some bits to support highpart
liveness information optimizations. It is about 100 lines of unidiff.
If someone is prepared to review the patch, I can extract an independent
patch against the then-current mainline.
--
Summary: delete_trivially_dead_insns fails to update the liveness
information
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Keywords: ice-checking
Severity: normal
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: amylaar at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
BugsThisDependsOn: 18992
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18995
