0006-GCSE-complex-constants.patch

[Maxim Kuvyrkov <maxim at codesourcery dot com>]

Certain architectures (e.g., ARM) cannot easily operate with constants, 
they need to emit sequences of several instructions to load constants 
into registers.  The common procedure to do this is to emit a (parallel 
[(set) (clobber (reg1)) ... (clobber (regN))]) instruction which later 
splits into several instructions using pseudos (regX) to store 
intermediate values.

Currently PRE and hoist do not GCSE constants, and there is a good 
reason for that, to avoid increasing register pressure; interestingly, 
symbol_refs are allowed to be GCSE'ed, is this intentional or by accident?

In any case, it seems like a good idea to GCSE constants and symbol_refs 
that need something beyond a simple (set) to get into a register, and 
not GCSE them otherwise.

This patch adds a simple heuristic to gcse.c:want_to_gcse_p() that 
adjusts preferences for CONST_INTs and SYMBOL_REFs.

OK to apply?

Thank you,

--
Maxim Kuvyrkov
CodeSourcery
maxim@codesourcery.com
(650) 331-3385 x724

Attachment: 0006-GCSE-complex-constants.ChangeLog
Description: Text document

Attachment: 0006-GCSE-complex-constants.patch
Description: Text document