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[Bug rtl-optimization/75964] insn combiner removes comparison after ABS
- From: "gjl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 09 Feb 2017 21:26:50 +0000
- Subject: [Bug rtl-optimization/75964] insn combiner removes comparison after ABS
- Auto-submitted: auto-generated
- References: <bug-75964-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=75964
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Eric Botcazou from comment #1)
> > After pass .combine, the 2nd comparison is missing, presumably because
> > combiner invokes signed overflow on ABS which does not apply because all
> > computations are performed as unsigned.
>
> Then you should have a warning with -Wstrict-overflow; this possibly comes
> from simplify-rtx.c:simplify_const_relational_operation in this case.
With -Wstrict-overflow=2 and avr-gcc-6.3 I get
warning: assuming signed overflow does not occur when assuming abs (x) >= 0 is
true [-Wstrict-overflow]
So it's not only wrong code but also wrong diagnostic...