Comment 5 for bug 1263576

seen in a segfault running the tests in the coinor-osi package,
https://launchpad.net/bugs/1263576, both in saucy and trusty, version 0.106.4
and 0.106.5. Version 0.103 doesn't show the issue.

both the 4.7 and 4.8 linaro branches show this behaviour, and trunk 20131121
(didn't build a newer one yet).

William Grant tracked that down to a bug with very negative vcall_offsets in
aarch64 multiple inheritance thunks. The example below has two consecutive
thunks, with the second adding 263 instead of subtracting 264.
aarch64_build_constant seems to not handle negative integers. He tried a quick
gcc patch to avoid using aarch64_build_constant, and the coinor-osi tests succeed.

0000000000401ca4 <_ZTv0_n256_N1C2adEv>:
  401ca4: f9400010 ldr x16, [x0]
  401ca8: f8500211 ldr x17, [x16,#-256]
  401cac: 8b110000 add x0, x0, x17
  401cb0: 17fffff9 b 401c94 <_ZN1C2adEv>

[...]

0000000000401cc4 <_ZTv0_n264_N1C2aeEv>:
  401cc4: f9400010 ldr x16, [x0]
  401cc8: d28020f1 mov x17, #0x107 // #263
  401ccc: f8716a11 ldr x17, [x16,x17]
  401cd0: 8b110000 add x0, x0, x17
  401cd4: 17fffff8 b 401cb4 <_ZN1C2aeEv>

Any chance for a quick 2013 review?

Thanks, Matthias

--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -2540,8 +2540,8 @@
    addr = plus_constant (Pmode, temp0, vcall_offset);
       else
  {
- aarch64_build_constant (IP1_REGNUM, vcall_offset);
- addr = gen_rtx_PLUS (Pmode, temp0, temp1);
+ aarch64_add_constant (IP0_REGNUM, IP1_REGNUM, vcall_offset);
+ addr = temp0;
  }

       aarch64_emit_move (temp1, gen_rtx_MEM (Pmode,addr));