On 09/09/15 22:51, Jeff Law wrote:
On 09/02/2015 07:43 AM, Kyrill Tkachov wrote:
+ rtx_code code; + if (val_a == -val_b)
Do we have to worry about signed overflow here? I'm thinking
specifically when val_b is the smallest possible integer
representable by a HOST_WIDE_INT. I suspect you may be able to
avoid these problems with judicious use of the hwi interfaces.
I understand the issue, but am not sure what hwi interfaces to use
here. Seems that the problem will be if val_b is HOST_WIDE_INT_MIN.
Right. When val_b is HOST_WIDE_INT_MIN, negating it will overflow.
Looking at the definition of abs_hwi in hwint.h before it negates
it's argument it asserts that it's not HOST_WIDE_INT_MIN. I think
that's to avoid this exact issue? If so, I've added a check for
HOST_WIDE_INT_MIN which should cover the undefined case when negating
a HOST_WIDE_INT, unless there's something else I'm missing.
That should be sufficient.
2015-09-02 Kyrylo Tkachov <kyrylo.tkac...@arm.com>
* ifcvt.c (noce_try_inverse_constants): New function.
(noce_process_if_block): Call it.
* optabs.h (emit_conditional_neg_or_complement): Declare prototype.
* optabs.def (negcc_optab, notcc_optab): Declare.
* optabs.c (emit_conditional_neg_or_complement): New function.
* doc/tm.texi (Standard Names): Document negcc, notcc names.
OK for the trunk.
Thanks for the review.
I'll commit it if/when the aarch64 and arm implementations of the hooks
in patches 2/3 and 3/3 are approved.
Kyrill
Thanks for your patience.
Jeff
