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From: richard@wetafx.co.nz To: gcc-gnats@gcc.gnu.org Subject: optimization/9641: const double arguments and -ffloat-store do not work together Date: Mon, 10 Feb 2003 07:56:00 -0000 [thread overview] Message-ID: <20030210075320.24402.qmail@sources.redhat.com> (raw) >Number: 9641 >Category: optimization >Synopsis: const double arguments and -ffloat-store do not work together >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: wrong-code >Submitter-Id: net >Arrival-Date: Mon Feb 10 07:56:00 UTC 2003 >Closed-Date: >Last-Modified: >Originator: richard@wetafx.co.nz >Release: gcc version 2.96 20000731 (Red Hat Linux 7.2 2.96-112.7.2) >Organization: >Environment: Linux 2.4.18-xfssmp #1 SMP i686 >Description: //////////main.c double rightfunc(double); double wrongfunc(double); int main(void) { rightfunc(0.75); wrongfunc(0.25); } //////////funcs.c double rightfunc(double t) { return t; } double wrongfunc(const double t) { return t; } //////////GNUmakefile all: wrong right right: main.c funcs.c; gcc -O3 -o $@ main.c funcs.c wrong: main.c funcs.c; gcc -O3 -ffloat-store -o $@ main.c funcs.c >How-To-Repeat: With the three supplied files, use gmake to build. The generated 'right' file works properly, but the generated 'wrong' file generates incorrect code for the 'wrongfunc' function: 0x8048474 <wrongfunc>: push %ebp 0x8048475 <wrongfunc+1>: mov %esp,%ebp 0x8048477 <wrongfunc+3>: sub $0x8,%esp 0x804847a <wrongfunc+6>: fldl 0xfffffff8(%ebp) 0x804847d <wrongfunc+9>: leave 0x804847e <wrongfunc+10>: ret 0x804847f <wrongfunc+11>: nop Basically, the code uses memory that has not be set to the value passed as a 'const double' argument. Note that rightfunc() has a double argument, while wrongfunc() has a const double argument. Otherwise they are the same. The 'wrong' file is built with -ffloat-store while the 'right' file is built without. >Fix: I can avoid 'const double' arguments, but this may mean some sifting through large code bases. I can avoid using -ffloat-store, but then I run into other code generation issues because of the broken nature how the optimizer handles comparisons with floats and doubles on Intel. >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2003-02-10 7:56 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2003-02-10 7:56 richard [this message] 2003-02-10 22:55 ehrhardt 2003-02-10 23:26 Richard Addison-Wood 2003-02-11 9:43 ehrhardt
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