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From: tevessen@pop-koeln.de To: gcc-gnats@gcc.gnu.org Subject: target/6041: x86: No inline FPU code generated even if arch says target always has FPU Date: Fri, 22 Mar 2002 08:46:00 -0000 [thread overview] Message-ID: <20020322163846.19506.qmail@sources.redhat.com> (raw) [-- Warning: decoded text below may be mangled, UTF-8 assumed --] [-- Attachment #1: Type: text/plain, Size: 2302 bytes --] >Number: 6041 >Category: target >Synopsis: x86: No inline FPU code generated even if arch says target always has FPU >Confidential: no >Severity: non-critical >Priority: medium >Responsible: unassigned >State: open >Class: pessimizes-code >Submitter-Id: net >Arrival-Date: Fri Mar 22 08:46:02 PST 2002 >Closed-Date: >Last-Modified: >Originator: Johannes Tevessen >Release: gcc version 3.0.3 >Organization: >Environment: Linux 2.4.17 #4 Mon Feb 18 12:29:18 CET 2002 i686 unknown BFD: GNU assembler version 2.11.90.0.8 (i386-redhat-linux) using BFD version 2.11.90.0.8 >Description: The info docs say: "`-mno-fancy-math-387' Some 387 emulators do not support the `sin', `cos' and `sqrt' instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD. As of revision 2.6.1, these instructions are not generated unless you also use the `-ffast-math' switch." Well, reading this made me curious and I wrote a simple piece of code like this: #include <math.h> double sindbl (double inp) { return sin (inp); } gives (-march=athlon -O9): sindbl: pushl %ebp movl %esp, %ebp subl $8, %esp leave jmp sin so there's actually a subfunction call to sin() generated for something that i586/i686/athlon/k6 can easily do with inline asm. -ffast-math changes this: sindbl: pushl %ebp movl %esp, %ebp fldl 8(%ebp) #APP fsin #NO_APP popl %ebp ret The point being that i586 upto athlon always include an FPU, so there's no need to look for FPU software emulator support unless explicitly wanted by the user. Also, -ffast-math turns on some more optimizations that may be unwanted. And: Maybe another bug: Just adding -mfancy-math-387 does _not_ produce inline asm as I had expected. It _also_ calls sin() in 3.0.3, so the docs are wrong here, too. >How-To-Repeat: Create any C file, #include <math.h>, use something like sin(), compile with optimization and -march=i686 (or similar) and inspect object file or gcc -S output. >Fix: Make inline FPU asm instructions the default for -march i586, i686, k6, athlon. >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2002-03-22 16:46 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-03-22 8:46 tevessen [this message] 2002-03-29 15:31 rth
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