http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49799
Carrot <carrot at google dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|target |rtl-optimization
--- Comment #4 from Carrot <carrot at google dot com> 2011-07-25 08:39:27 UTC
---
After some combine, gcc gets the following expression
(ashiftrt:SI (ashift:SI (reg:SI 145 [ *K_2(D) ])
(const_int -1 [0xffffffffffffffff]))
(const_int 16 [0x10]))
Then gcc tries to simplify it by calling make_compound_operation, in this
function at line 7786, it detects the cases that shift left and right and
replaces it with bit field extraction. It is a good optimization for usual
cases. But for this ill formed case, we can't make a valid bit field extraction
since we don't know what's the target field.
Add the following condition for the transformation should prevent the illegal
instruction.
INTVAL (XEXP (lhs, 1)) >= 0
