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From: Richard Earnshaw <rearnsha@arm.com> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: target/5170: Supicious code in arm.md Date: Fri, 04 Jan 2002 09:46:00 -0000 [thread overview] Message-ID: <20020104174602.18327.qmail@sources.redhat.com> (raw) The following reply was made to PR target/5170; it has been noted by GNATS. From: Richard Earnshaw <rearnsha@arm.com> To: Klaus.k.pedersen@nokia.com Cc: gcc-gnats@gcc.gnu.org, Richard.Earnshaw@arm.com Subject: Re: target/5170: Supicious code in arm.md Date: Fri, 04 Jan 2002 17:41:38 +0000 > I think that there is a bug here: > > > for (i = 0; i < 25; i++) > > if ((val & (mask << i)) == val) > > break; > > > > if (i == 0) > > FAIL; The test is correct. We don't want to use the split pattern if we can handle the constant with a single instruction. That could lead to a recursive split of the instruction. That is, the pattern is looking for cases of mov Rn, #const that are invalid, but can be represented as mov Rn, #(const >> i) lsr Rn, #i Clearly we don't want to do this when i == 0, since a shift of zero is a no-op (and recursive attempts to split the initial mov instruction would never terminate). There is no need to test for i == 25, since the predicate for the pattern has already told us that the constant is OK.
next reply other threads:[~2002-01-04 17:46 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-01-04 9:46 Richard Earnshaw [this message] -- strict thread matches above, loose matches on Subject: below -- 2002-03-15 9:18 rearnsha 2002-01-24 2:30 rearnsha 2002-01-23 11:16 Klaus Pedersen 2002-01-22 3:04 pb 2002-01-04 9:46 Richard Earnshaw 2001-12-21 6:56 Klaus.k.pedersen
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