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* [Bug target/54461] New: [avr] add configure option for better AVR-Libc integration
@ 2012-09-02 19:32 gjl at gcc dot gnu.org
  2012-09-02 19:34 ` [Bug target/54461] " gjl at gcc dot gnu.org
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: gjl at gcc dot gnu.org @ 2012-09-02 19:32 UTC (permalink / raw)
  To: gcc-bugs

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54461

             Bug #: 54461
           Summary: [avr] add configure option for better AVR-Libc
                    integration
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: gjl@gcc.gnu.org
        ReportedBy: gjl@gcc.gnu.org
            Target: avr


For historical reasons, AVR-Libc implements functions that GCC expects to live
in libgcc, namely float functions like __fixsfsi.

Currently, avr-gcc is not configurable to accommodate that situation which
leads to performance loss if the float support functions from libgcc are used.

This happens at least in the following situations:

* The user does not specify -lm.  -lm should only be needed
  if function from math.h are used, not for language core
  features like int i = (int) float.

* The application is LTO compiled, i.e. linked with -flto.
  The plugin machinery passes lgcc -lc lgcc through to the
  linker by means of -plugin-opt=-pass-through=-lgcc etc.
  so that -lgcc is linked prior to -lm.

* The user uses fixed <-> float conversion routines from
  libgcc.  These routines refer float functions, and the linker
  resolves these function in libgcc if they are there.

* avr-g++ is used as linker driver.

See also PR28718 and
http://lists.gnu.org/archive/html/avr-gcc-list/2012-08/msg00070.html


^ permalink raw reply	[flat|nested] 7+ messages in thread

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Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2012-09-02 19:32 [Bug target/54461] New: [avr] add configure option for better AVR-Libc integration gjl at gcc dot gnu.org
2012-09-02 19:34 ` [Bug target/54461] " gjl at gcc dot gnu.org
2012-09-05  8:48 ` gjl at gcc dot gnu.org
2012-09-05 12:20 ` gjl at gcc dot gnu.org
2012-09-05 12:23 ` gjl at gcc dot gnu.org
2012-09-05 13:03 ` gjl at gcc dot gnu.org
2013-01-07 16:23 ` gjl at gcc dot gnu.org

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