If-conversion and conditional move.

[Dan Towner]

Hi all,

I have recently been adding conditional move instructions to a GCC port 
for a 16-bit DSP (i.e., movhicc, etc.). The DSP only supports 
move-on-equals and move-on-not-equals, not the whole variety of LE, GT, 
LEU, and so on. The movhicc pattern itself is written to fail if an 
attempt is  made to generate a conditional move using an unsupported 
comparison, but the if-conversion code (ifcvt.c) doesn't seem to check 
that a valid comparison is used. For example, if a simple code block is 
found with a GT comparison controlling entry, the if-conversion code 
attempts to generate a conditional move for a GT comparison, which isn't 
supported. However, rather than giving up, and not performing the 
conversion, the if-conversion code aborts instead.

What is the easiest way to go about solving this problem?
   1) change the abort to allow graceful failure, with
      fallback to using branches
   2) prevent the if-conversion from even being attempted when an
      unsupported comparison is used?

thanks,

dan.

=============================================================================
Daniel Towner
picoChip Designs Ltd., Riverside Buildings, 108, Walcot Street, BATH, 
BA1 5BG
dant@picochip.com
07786 702589