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Re: optimization/7799: [3.2/3.3 regression] Loop bug with optimization flag -Os in gcc
- From: Eric Botcazou <ebotcazou at libertysurf dot fr>
- To: "Christian Ehrhardt" <ehrhardt at mathematik dot uni-ulm dot de>
- Cc: nejataydin at superonline dot com,gcc-gnats at gcc dot gnu dot org,gcc at gcc dot gnu dot org,gcc-bugs at gcc dot gnu dot org,nobody at gcc dot gnu dot org
- Date: Fri, 13 Dec 2002 14:49:01 +0100
- Subject: Re: optimization/7799: [3.2/3.3 regression] Loop bug with optimization flag -Os in gcc
- References: <20021213133626.29733.qmail@theseus.mathematik.uni-ulm.de>
> This transformation is IMHO illegal because there is no way to make the
> comparison in general equivialent to that in the original for loop.
> If p is initially 0x7ffffffc the comparison must be treated as unsigned,
> however, if p is initially 0xfffffffc the comparison must be treated as
> signed.
Well-known deficiency of the strength reduction pass (see the testcase
testsuite/gcc.c-torture/execute/loop-2e.c which is XFAILed on x86 at -Os).
--
Eric Botcazou