https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79279
Bug ID: 79279
Summary: combine/simplify_set: wrong call to
REG_CANNOT_CHANGE_MODE_P
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: aurelien.buhrig.gcc at gmail dot com
Target Milestone: ---
Created attachment 40619
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40619&action=edit
patch
In simplify_set, when trying to generate paradoxical subregs of hard regs,
a call to REG_CANNOT_CHANGE_MODE_P enables checking if the new mode is valid.
In fact, changing from (set x:m1 (subreg:m1 (op:m2))) to (set (subreg:m2 x)
op2) is valid if REG_CANNOT_CHANGE_MODE_P (REGNO(x), FROM=m1, TO=m2) is false.
Currently, FROM and TO parameters are switched, leading in wrong combination of
sub words paradoxical subregs (private target backend):
Currently:
&& REG_CANNOT_CHANGE_MODE_P (REGNO (dest),
GET_MODE (SUBREG_REG (src)),
GET_MODE (src)))
Should be:
&& REG_CANNOT_CHANGE_MODE_P (REGNO (dest),
GET_MODE (src),
GET_MODE (SUBREG_REG (src))))
See attached patch.
