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From: "arseny.klimovsky at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/46993] New: Optimization on i386 lead to user-visible traps during floating-point operations Date: Fri, 17 Dec 2010 16:34:00 -0000 [thread overview] Message-ID: <bug-46993-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46993 Summary: Optimization on i386 lead to user-visible traps during floating-point operations Product: gcc Version: 4.5.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target AssignedTo: unassigned@gcc.gnu.org ReportedBy: arseny.klimovsky@gmail.com Version: $ g++-4.5.2 -v Using built-in specs. COLLECT_GCC=g++-4.5.2 COLLECT_LTO_WRAPPER=/opt/gcc-4.5.2/libexec/gcc/x86_64-unknown-linux-gnu/4.5.2/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../gcc-4.5.2/configure --prefix /opt/gcc-4.5.2/ Thread model: posix gcc version 4.5.2 (GCC) Command: $ g++ -m32 -fsignaling-nans -O1 -c -S -o simple.s simple.cpp Consider a simple function, which copies one value from double array c to double array a. #include <string.h> void copy (double * a, double * c) { double b[100]; memcpy (b, c, sizeof (double)); memcpy (a, b, sizeof (double)); } This will generate code .cfi_startproc pushl %ebp .cfi_def_cfa_offset 8 movl %esp, %ebp .cfi_offset 5, -8 .cfi_def_cfa_register 5 movl 12(%ebp), %eax fldl (%eax) movl 8(%ebp), %eax fstpl (%eax) popl %ebp .cfi_restore 5 .cfi_def_cfa 4, 4 ret .cfi_endproc Here, if c[0] is a NaN, and FPU exception mask is set, an FPE will occur. In gcc 4.4 and earlier I could use memcpy instead of operator= to be sure, that no floating point operations will be generated. Now I don't know how to safely copy values from local double buffer (or a single variable) to some address without floating point operations.
next reply other threads:[~2010-12-17 16:34 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-12-17 16:34 arseny.klimovsky at gmail dot com [this message] 2011-01-12 12:05 ` [Bug target/46993] " arseny.klimovsky at gmail dot com 2024-03-12 22:12 ` pinskia at gcc dot gnu.org
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