Hi,
With the aarch64_cm<optab>di patterns a bug was introduced. While the
unsplit versions of these patterns, which operate in the
SIMD register set, do not clobber CC_REGNUM, the split versions, which
operate in the general purpose register set, do clobber CC_REGNUM.
This causes a problem if scheduling rearranges the unsplit version
of these instructions. For example, if we have:
aarch64_cmeqdi_unsplit
set_cc_flags
jump
Then we could schedule as
set_cc_flags
aarch64_cmeqdi_unsplit
jump
Because the unsplit version does not clobber CC_REGNUM.
If we now decide to split we get:
set_cc_flags
aarch64_cmeqdi_set_cc_flags
aarch64_cmeqdi_use_cc_flags
jump
And the jump uses the wrong value for cc_flags.
We fix this problem by adding the clobber of CC_REGNUM to
the aarch64_cm<optab>di patterns. This may restrict the
scheduling opportunities available, but should prevent
incorrect code generation.
Tested on aarch64-none-linux-gnu, aarch64-none-elf with no
regressions. The bug manifest itself in the libstdc++ testsuite,
so I've double checked there to ensure that the bug has cleared.
Thanks,
James
---
gcc/
2013-05-17 James Greenhalgh <james.greenhalgh@arm.com>
* config/aarch64/aarch64-simd.md
(aarch64_cm<optab>di): Add clobber of CC_REGNUM to unsplit pattern.