diff mbox series

[committed] i386: Remove unneeded assignments when triggering SSE exceptions

Message ID CAFULd4bDMW1WD1xYaOD54Hir5nx7OHdVXzg2H7-2+zYwKC_6RA@mail.gmail.com
State New
Headers show
Series [committed] i386: Remove unneeded assignments when triggering SSE exceptions | expand

Commit Message

Uros Bizjak April 19, 2020, 12:19 p.m. UTC 
According to "Intel 64 and IA32 Arch SDM, Vol. 3:

"Because SIMD floating-point exceptions are precise and occur immediately,
the situation does not arise where an x87 FPU instruction, a WAIT/FWAIT
instruction, or another SSE/SSE2/SSE3 instruction will catch a pending
unmasked SIMD floating-point exception."

This is also confirmed by the following testcase:

--cut here--

#define _GNU_SOURCE
#include <fenv.h>
#include <signal.h>
#include <stddef.h>
#include <stdlib.h>

static int counter;

void
__attribute__((noinline))
__divbyzero_ex (void)
{
  float f = 1.0f, g = 0.0f;
#ifdef __SSE_MATH__
  asm volatile ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
#else
  asm volatile ("fdivp\t%1" : "+t" (f) : "u" (g) : "st(1)");
  /* No need for fwait, exception is triggered by emitted fstp.  */
#endif
}

void handler (int i)
{
  exit (0);
}

int
main ()
{
  struct sigaction s;
  sigemptyset (&s.sa_mask);
  s.sa_handler = handler;
  s.sa_flags = 0;
  sigaction (SIGFPE, &s, NULL);

  feenableexcept (FE_DIVBYZERO);

  __divbyzero_ex ();

  abort ();
}
--cut here--

libgcc/ChangeLog:

2020-04-19  Uroš Bizjak  <ubizjak@gmail.com>

    * config/i386/sfp-exceptions.c (__sfp_handle_exceptions) [__SSE_MATH__]:
    Remove unneeded assignments to volatile memory.

libatomic/ChangeLog:

2020-04-19  Uroš Bizjak  <ubizjak@gmail.com>

    * config/x86/fenv.c (__atomic_feraiseexcept) [__SSE_MATH__]:
    Remove unneeded assignments to volatile memory.

libgfortran/ChangeLog:

2020-04-19  Uroš Bizjak  <ubizjak@gmail.com>

    * config/fpu-387.h (local_feraiseexcept) [__SSE_MATH__]:
    Remove unneeded assignments to volatile memory.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Committed to mainline.

Uros.
diff mbox series

Patch

diff --git a/libatomic/config/x86/fenv.c b/libatomic/config/x86/fenv.c
index 7828162c68b..d7b1bbe5ea1 100644
--- a/libatomic/config/x86/fenv.c
+++ b/libatomic/config/x86/fenv.c
@@ -57,9 +57,7 @@  __atomic_feraiseexcept (int excepts)
     {
       float f = 0.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       asm volatile ("%vdivss\t{%0, %d0|%d0, %0}" : "+x" (f));
-      r = f; /* Needed to trigger exception.   */
 #else
       asm volatile ("fdiv\t{%y0, %0|%0, %y0}" : "+t" (f));
       /* No need for fwait, exception is triggered by emitted fstp.  */
@@ -77,9 +75,7 @@  __atomic_feraiseexcept (int excepts)
     {
       float f = 1.0f, g = 0.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       asm volatile ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
-      r = f; /* Needed to trigger exception.   */
 #else
       asm volatile ("fdivs\t%1" : "+t" (f) : "m" (g));
       /* No need for fwait, exception is triggered by emitted fstp.  */
@@ -105,9 +101,7 @@  __atomic_feraiseexcept (int excepts)
     {
       float f = 1.0f, g = 3.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       asm volatile ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
-      r = f; /* Needed to trigger exception.   */
 #else
       asm volatile ("fdivs\t%1" : "+t" (f) : "m" (g));
       /* No need for fwait, exception is triggered by emitted fstp.  */
diff --git a/libgcc/config/i386/sfp-exceptions.c b/libgcc/config/i386/sfp-exceptions.c
index c994491c650..31a24ced704 100644
--- a/libgcc/config/i386/sfp-exceptions.c
+++ b/libgcc/config/i386/sfp-exceptions.c
@@ -48,9 +48,7 @@  __sfp_handle_exceptions (int _fex)
     {
       float f = 0.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       asm volatile ("%vdivss\t{%0, %d0|%d0, %0}" : "+x" (f));
-      r = f; /* Needed to trigger exception.   */
 #else
       asm volatile ("fdiv\t{%y0, %0|%0, %y0}" : "+t" (f));
       /* No need for fwait, exception is triggered by emitted fstp.  */
@@ -68,9 +66,7 @@  __sfp_handle_exceptions (int _fex)
     {
       float f = 1.0f, g = 0.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       asm volatile ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
-      r = f; /* Needed to trigger exception.   */
 #else
       asm volatile ("fdivs\t%1" : "+t" (f) : "m" (g));
       /* No need for fwait, exception is triggered by emitted fstp.  */
@@ -96,9 +92,7 @@  __sfp_handle_exceptions (int _fex)
     {
       float f = 1.0f, g = 3.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       asm volatile ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
-      r = f; /* Needed to trigger exception.   */
 #else
       asm volatile ("fdivs\t%1" : "+t" (f) : "m" (g));
       /* No need for fwait, exception is triggered by emitted fstp.  */
diff --git a/libgfortran/config/fpu-387.h b/libgfortran/config/fpu-387.h
index 623e878b482..13be2045b72 100644
--- a/libgfortran/config/fpu-387.h
+++ b/libgfortran/config/fpu-387.h
@@ -103,9 +103,7 @@  local_feraiseexcept (int excepts)
     {
       float f = 0.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       __asm__ __volatile__ ("%vdivss\t{%0, %d0|%d0, %0}" : "+x" (f));
-      r = f; /* Needed to trigger exception.   */
 #else
       __asm__ __volatile__ ("fdiv\t{%y0, %0|%0, %y0}" : "+t" (f));
       /* No need for fwait, exception is triggered by emitted fstp.  */
@@ -123,9 +121,7 @@  local_feraiseexcept (int excepts)
     {
       float f = 1.0f, g = 0.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       __asm__ __volatile__ ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
-      r = f; /* Needed to trigger exception.   */
 #else
       __asm__ __volatile__ ("fdivs\t%1" : "+t" (f) : "m" (g));
       /* No need for fwait, exception is triggered by emitted fstp.  */
@@ -151,9 +147,7 @@  local_feraiseexcept (int excepts)
     {
       float f = 1.0f, g = 3.0f;
 #ifdef __SSE_MATH__
-      volatile float r __attribute__ ((unused));
       __asm__ __volatile__ ("%vdivss\t{%1, %d0|%d0, %1}" : "+x" (f) : "xm" (g));
-      r = f; /* Needed to trigger exception.   */
 #else
       __asm__ __volatile__ ("fdivs\t%1" : "+t" (f) : "m" (g));
       /* No need for fwait, exception is triggered by emitted fstp.  */