http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49903
Summary: AVR: Redundant comparisons in binary-seach switch/case
expansion
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: g...@gcc.gnu.org
CC: eric.wedding...@atmel.com
Target: avr
Created attachment 24864
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24864
cswitch.c: C test case
avr-gcc emits redundant comparisons like these:
cpi r24,lo8(55) ; 22 *cmpqi/3 [length = 1]
breq .L10 ; 23 branch [length = 1]
cpi r24,lo8(56) ; 24 *cmpqi/3 [length = 1]
brge .L19 ; 25 branch [length = 1]
which could just as well be
cpi r24,lo8(55) ; 22 *cmpqi/3 [length = 1]
breq .L10 ; 23 branch [length = 1]
brge .L19 ; 25 branch [length = 1]
or these:
cpi r24,lo8(100) ; 61 *cmpqi/3 [length = 1]
breq .L16 ; 62 branch [length = 1]
cpi r24,lo8(100) ; 63 *cmpqi/3 [length = 1]
brlt .L15 ; 64 branch [length = 1]
which could just as well be
cpi r24,lo8(100) ; 61 *cmpqi/3 [length = 1]
breq .L16 ; 62 branch [length = 1]
brlt .L15 ; 64 branch [length = 1]
This concernes signed/unsigned comparisons for QI/HI/SI
-- command line ----------------------------------------------
avr-gcc cswitch.c -dp -S -Os
-- configure -------------------------------------------------
../../gcc.gnu.org/trunk/configure --target=avr
--prefix=/home/john/gnu/install/gcc-4.7 --disable-nls --disable-shared
--enable-languages=c,c++ --with-dwarf2 --disable-lto
-- GCC -------------------------------------------------
as of 4.7.0 trunk, r176818 from 2011-07-27
