[Bug rtl-optimization/57046] [4.8/4.9 Regression] wrong code generated by gcc 4.8.0 on i686

2013-04-23 Thread jakub at gcc dot gnu.org 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57046



Jakub Jelinek jakub at gcc dot gnu.org changed:



   What|Removed |Added



   Priority|P3  |P1

 CC||jakub at gcc dot gnu.org,

   ||vmakarov at gcc dot gnu.org

  Component|c   |rtl-optimization



--- Comment #3 from Jakub Jelinek jakub at gcc dot gnu.org 2013-04-23 
12:09:58 UTC ---

Started with http://gcc.gnu.org/r192719 aka LRA merge, the problematic function

is emac_operation.

[Bug rtl-optimization/57046] [4.8/4.9 Regression] wrong code generated by gcc 4.8.0 on i686

2013-04-23 Thread jakub at gcc dot gnu.org 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57046



--- Comment #4 from Jakub Jelinek jakub at gcc dot gnu.org 2013-04-23 
12:26:35 UTC ---

We have after the get_value call:

(insn 73 30 32 6 (set (reg:SI 76 [ D.1441 ])

(reg:SI 0 ax)) pr57046.c:42 85 {*movsi_internal}

 (expr_list:REG_DEAD (reg:SI 0 ax)

(nil)))

(insn 32 73 33 6 (parallel [

(set (reg:SI 73 [ D.1443 ])

(ashift:SI (subreg:SI (reg:DI 60 [ D.1441 ]) 0)

(const_int 2 [0x2])))

(clobber (reg:CC 17 flags))

]) 502 {*ashlsi3_1}

 (expr_list:REG_DEAD (reg:DI 60 [ D.1441 ])

(expr_list:REG_UNUSED (reg:CC 17 flags)

(nil



and IRA decides to put pseudo 76 into %ebx and pseudo 60 into %ecx.  Either it

is an IRA bug, or IRA takes into account that we only really need the low

32-bits of pseudo 60 at that point.  In any case, reload loads SImode %ecx from

the stack and uses it in the shift, while LRA loads full DImode %ecx (i.e. %ecx

and %ebx) from the stack, then uses just the low bits from that (i.e. %ecx) in

the shift.  So the LRA generated code clobbers the value in %ebx, and get_value

call is even later on DCEd because of it.

[Bug rtl-optimization/57046] [4.8/4.9 Regression] wrong code generated by gcc 4.8.0 on i686

2013-04-23 Thread vmakarov at redhat dot com 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57046



Vladimir Makarov vmakarov at redhat dot com changed:



   What|Removed |Added



 CC||vmakarov at redhat dot com



--- Comment #5 from Vladimir Makarov vmakarov at redhat dot com 2013-04-23 
15:34:40 UTC ---

(In reply to comment #4)

 We have after the get_value call:

 (insn 73 30 32 6 (set (reg:SI 76 [ D.1441 ])

 (reg:SI 0 ax)) pr57046.c:42 85 {*movsi_internal}

  (expr_list:REG_DEAD (reg:SI 0 ax)

 (nil)))

 (insn 32 73 33 6 (parallel [

 (set (reg:SI 73 [ D.1443 ])

 (ashift:SI (subreg:SI (reg:DI 60 [ D.1441 ]) 0)

 (const_int 2 [0x2])))

 (clobber (reg:CC 17 flags))

 ]) 502 {*ashlsi3_1}

  (expr_list:REG_DEAD (reg:DI 60 [ D.1441 ])

 (expr_list:REG_UNUSED (reg:CC 17 flags)

 (nil

 

 and IRA decides to put pseudo 76 into %ebx and pseudo 60 into %ecx.  Either it

 is an IRA bug, or IRA takes into account that we only really need the low

 32-bits of pseudo 60 at that point.  In any case, reload loads SImode %ecx 
 from

 the stack and uses it in the shift, while LRA loads full DImode %ecx (i.e. 
 %ecx

 and %ebx) from the stack, then uses just the low bits from that (i.e. %ecx) in

 the shift.  So the LRA generated code clobbers the value in %ebx, and 
 get_value

 call is even later on DCEd because of it.



It seems like a discrepancy in IRA which allocates in terms of subregisters and

LRA splitting (including call save/restore as in this case) in terms of

pseudos.  I guess fixing this might take about week.