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From: "Thomas dot Koenig at online dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/20517] New: bit shift/mask optimization potential Date: Thu, 17 Mar 2005 13:17:00 -0000 [thread overview] Message-ID: <20050317131718.20517.Thomas.Koenig@online.de> (raw) $ cat shift.c #include <stdio.h> #define OFFSET 4 #define MASK 0xf0 int main() { unsigned int f,g; scanf("%u",&f); if ((f & MASK) >> OFFSET == 1) { printf("success\n"); } return 0; } $ gcc -S -O2 -fdump-tree-optimized shift.c $ tail -20 shift.c.t66.optimized unsigned int g; unsigned int f; int D.1807; unsigned int D.1806; unsigned int D.1805; unsigned int f.10; <bb 0>: scanf (&"%u"[0], &f); if ((f & 240) >> 4 == 1) goto <L0>; else goto <L1>; <L0>:; printf (&"success\n"[0]); <L1>:; return 0; } $ gcc -v Using built-in specs. Target: ia64-unknown-linux-gnu Configured with: ../gcc-4.1-20050306/configure --prefix=/home/zfkts --enable-languages=c,f95 --disable-optimization Thread model: posix gcc version 4.1.0 20050306 (experimental) The expression (f & 0xf0) >> 4 == 1 could be optimized to f & 0xf == 1 << 4. Code like that occurs in the libgfortan library. -- Summary: bit shift/mask optimization potential Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P2 Component: middle-end AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: Thomas dot Koenig at online dot de CC: gcc-bugs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20517
next reply other threads:[~2005-03-17 13:17 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2005-03-17 13:17 Thomas dot Koenig at online dot de [this message] 2005-03-17 13:34 ` [Bug middle-end/20517] " Thomas dot Koenig at online dot de 2005-03-17 17:21 ` [Bug tree-optimization/20517] " pinskia at gcc dot gnu dot org 2005-07-23 21:07 ` phython at gcc dot gnu dot org
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