[Bug middle-end/54821] New: Microblaze: Position independent code for byte access is incorrect.

[Bug middle-end/54821] New: Microblaze: Position independent code for byte access is incorrect.

[qball at sarine dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54821

             Bug #: 54821
           Summary: Microblaze: Position independent code for byte access
                    is incorrect.
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: qball@sarine.nl


When enabling position independent code gcc generates incorrect assembly for
byte access. Works fine when generating word (32bit) loads/writes.

e.g. 
When doing a word load results in the following correct assembly:
             lwi          r3, r20, 20            # load the address at .got.plt
+ 20 (address of a variable in the .got section)
             lwi          r4, r3, 0                 # load the value of the
variable in r4

However when doing byte load:

            imm       4                          
            lbui        r3, r20, 23884     # load the value of the variable in
r3. The address used is r20 + 0x45d4c.

There are 2 things going wrong..  
1.) It tries to load the r20 + the absolute offset of the variable.
2.) It should first load the address (from the got) then load the value from
that address
I would expect something like:
lwi         r3, r20, 16
lbui        r4, r3, 0

A similar things goes wrong for half word access.


This problem can be reproduced with GCC 4.1.2 (from xilinx) up to 4.7.2 (When
looking in the object files, generating elf files fails as of bug #54819)
A script to build the cross-compiler can be found here:
https://github.com/DaveDavenport/CrossCompilerGCCScript/blob/master/gcc_cross_compiler.sh

C code that shows the issue:
char temp = 3;
int temp2 = 12;
short int temp4 =13;
void main()
{
    int a = temp+ temp2+temp4;
}


Output generated for this: (by 4.1.2)
000001b0 <main>:
 1b0:    3021fff0     addik    r1, r1, -16
 1b4:    fa610008     swi    r19, r1, 8
 1b8:    fa81000c     swi    r20, r1, 12
 1bc:    12610000     addk    r19, r1, r0
 1c0:    e0740444     lbui    r3, r20, 1092
 1c4:    90630060     sext8    r3, r3
 1c8:    10830000     addk    r4, r3, r0
 1cc:    b0000000     imm    0
 1d0:    e874000c     lwi    r3, r20, 12
 1d4:    e8630000     lwi    r3, r3, 0
 1d8:    10841800     addk    r4, r4, r3
 1dc:    e474044c     lhui    r3, r20, 1100
 1e0:    90630061     sext16    r3, r3
 1e4:    10641800     addk    r3, r4, r3
 1e8:    f8730004     swi    r3, r19, 4
 1ec:    10330000     addk    r1, r19, r0
 1f0:    ea610008     lwi    r19, r1, 8
 1f4:    ea81000c     lwi    r20, r1, 12
 1f8:    30210010     addik    r1, r1, 16
 1fc:    b60f0008     rtsd    r15, 8
 200:    80000000     or    r0, r0, r0


Only the load word is done correctly.

[Bug middle-end/54821] Microblaze: Position independent code for byte access is incorrect.

[qball at sarine dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54821

--- Comment #1 from qball at sarine dot nl 2012-10-05 13:17:17 UTC ---
For 4.6.2 (xilinx) this seems to fix the code generation:
mb_gnu/src/gcc/gcc/config/microblaze/microblaze.c
temp/mb_gnu/src/gcc/gcc/config/microblaze/microblaze.c
@@ -558,7 +558,7 @@
       {
         return !(flag_pic && pic_address_needs_scratch (x));
       }
-    else if (flag_pic == 2)
+    else if (flag_pic)
       {
         return false;
       }

Generates:
    addik    r1,r1,-16
    swi    r19,r1,8
    swi    r20,r1,12
    addk    r19,r1,r0
    lwi    r3,r20,temp@GOT
    lbui    r3,r3,0
    sext8    r3,r3
    addk    r4,r3,r0
    lwi    r3,r20,temp2@GOT
    lwi    r3,r3,0
    addk    r4,r4,r3
    lwi    r3,r20,temp4@GOT
    lhui    r3,r3,0
    sext16    r3,r3
    addk    r3,r4,r3
    swi    r3,r19,4
    addk    r1,r19,r0
    lwi    r19,r1,8
    lwi    r20,r1,12
    addik    r1,r1,16
    rtsd    r15,8
    nop        # Unfilled delay slot

[Bug target/54821] Microblaze: Position independent code for byte access is incorrect.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54821

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |Microblaze
          Component|middle-end                  |target
           Severity|major                       |normal