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Re: [patch committed] Defaulting to -fno-ira-share-spill-slots on SH

Kaz Kojima wrote:

PR 37514 is a wrong-code problem on SH which is a 4.4 regression
started after the IRA merge.  IRA makes spill slots shared if
possible when flag_ira_share_spill_slots set.  In the above PR,
it causes a wrong sharing of slots on SH.  I've been trying to
see why this sharing occurs but it's a hard problem for me.
With -fno-ira-share-spill-slots, the problem goes away, though
it increases the code sizes of several tests in CSiBE by ~10%.
Although this code size regression isn't ignorable, I think
that the wrong code problem is far bigger than that.  I'd like
to work around this PR by defaulting to -fno-ira-share-spill-slots
on this target.  The attached patch is for this.  The patch also
adds a new target specific test to remember that the PR isn't fixed
yet.  It's tested with bootstrap and the top level "make -k check"
on sh4-unknown-linux-gnu.  The testsuite change is tested also
on i686-pc-linux-gnu.

2008-11-10  Kaz Kojima  <>

PR rtl-optimization/37514
* config/sh/sh.h (OPTIMIZATION_OPTIONS): Set
flag_ira_share_spill_slots to 2 if it's already non-zero.
(OVERRIDE_OPTIONS): Clear flag_ira_share_spill_slots if
flag_ira_share_spill_slots is 2.
Seems like absolutely the wrong approach to me. I'm surprised we're still having stack slot sharing problems with the patch for 37447 installed.


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