Mainline bootstrap failure on ia64

[Jim Wilson]

Andreas Schwab wrote:
> Mainline does not bootstrap on ia64 because -frename-registers is now the
> default.

The problem is that the IA-64 port uses the common idiom of leaving off 
the constraints for op0 of a call_value pattern, so that we can accept 
any return rtx.  In particular, we need to accept PARALLEL here which is 
not an ordinary operand.  However, the lack of constraints means we have 
an output operand with no "=".

regrename handles conditional execution by identifying output operands 
(i.e. operands with = constraints), and then changing them to in-out 
operands if they occured inside a COND_EXEC.  This fails when we have a 
call_value pattern inside a COND_EXEC because the = constraint is 
missing, so this operand does not get changed to an in-out operand.

This can be fixed by changing the call_value op0 constraints to "=X,X". 
  It looks a bit odd to use using X outside a match_scratch, but it 
seems to do what I want, i.e. accept all operands, even things that 
don't look like operands like PARALLEL.

Any other target that uses COND_EXEC and drops the constraints for op0 
of a call_value pattern will run into the same problem.  Perhaps we 
should go through and fix all md files to use =X constraints here.

This patch works for the libstdc++-v3/src/wlocal-inst.cc testcase which 
is the first failure I saw when doing an IA-64 bootstrap.  I haven't 
done any further testing yet.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com
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