[Bug bootstrap/44255] [4.6 regression] gcc-4.6-20100522 bootstrap comparison failure on sparc64 and arm

[mikpe at it dot uu dot se]

------- Comment #5 from mikpe at it dot uu dot se  2010-05-24 16:21 -------
Comparing stage2-libiberty/cp-demangle.o with stage3-libiberty/cp-demangle.o
shows that one instruction has had it's source operands swapped:

> objdump -d stage2-libiberty/cp-demangle.o > a
> objdump -d stage3-libiberty/cp-demangle.o > b
> diff -u a b
--- a   2010-05-24 17:59:49.000000000 +0200
+++ b   2010-05-24 17:59:54.000000000 +0200
@@ -1,5 +1,5 @@

-stage2-libiberty/cp-demangle.o:     file format elf32-sparc
+stage3-libiberty/cp-demangle.o:     file format elf32-sparc


 Disassembly of section .text:
@@ -4702,7 +4702,7 @@
     5078:      89 29 20 04     sll  %g4, 4, %g4
     507c:      84 00 80 04     add  %g2, %g4, %g2
     5080:      84 00 b8 6c     add  %g2, -1940, %g2
-    5084:      84 80 80 03     addcc  %g2, %g3, %g2
+    5084:      84 80 c0 02     addcc  %g3, %g2, %g2
     5088:      22 80 02 11     be,a   58cc <cplus_demangle_type+0xa20>
     508c:      c4 00 a0 04     ld  [ %g2 + 4 ], %g2
     5090:      c6 06 20 14     ld  [ %i0 + 0x14 ], %g3

Now, the code is still correct, but gcc shouldn't arbitrarily change it's mind
like this in stage3. Hence I suspect r159600 introduces some non-determinism,
or exposes latent non-determinism.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44255