[Bug rtl-optimization/36884] ifcvt poor optimization

["gjl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36884

--- Comment #4 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-05 13:20:15 UTC ---
Created attachment 24691
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24691
C Testcase pr36884.c

This testcase shows the dis-optimization in 4.7. trunk

======================================================
Compiled with -O2 -S:

swap:
    mov r18,r25
    rol r18
    clr r18
    rol r18
    ldi r19,lo8(0)
    clr __tmp_reg__
    lsr r19
    ror r18
    ror __tmp_reg__
    lsr r19
    ror r18
    ror __tmp_reg__
    mov r19,r18
    mov r18,__tmp_reg__
    sbrc r25,6
    ori r19,hi8(8192)
.L3:
    sbrc r25,5
    ori r19,hi8(16384)
.L4:
    sbrc r25,4
    ori r19,hi8(-32768)
.L5:
    mov r24,r18
    mov r25,r19
    ret

======================================================
Compiled with -O2 -S -fno-if-conversion:

swap:
    sbrc r25,7
    rjmp .L6
    ldi r18,lo8(0)
    ldi r19,hi8(0)
.L2:
    sbrc r25,6
    ori r19,hi8(8192)
.L3:
    sbrc r25,5
    ori r19,hi8(16384)
.L4:
    sbrc r25,4
    ori r19,hi8(-32768)
.L5:
    mov r24,r18
    mov r25,r19
    ret
.L6:
    ldi r18,lo8(64)
    ldi r19,hi8(64)
    rjmp .L2

======================================================

The compiler does a lengthy extract and reuse of the MSB.