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GNU C Library master sources branch release/2.26/master updated. glibc-2.26-42-g548cc83

From: jsm28 at sourceware dot org
To: glibc-cvs at sourceware dot org
Date: 28 Sep 2017 02:03:40 -0000
Subject: GNU C Library master sources branch release/2.26/master updated. glibc-2.26-42-g548cc83
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The branch, release/2.26/master has been updated
       via  548cc83c38a91852b1e44045ead3d20ccd5db4cf (commit)
      from  d37c951fde57e8acb320a9a7d437ba50a1fc3c8a (commit)

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- Log -----------------------------------------------------------------
http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=548cc83c38a91852b1e44045ead3d20ccd5db4cf

commit 548cc83c38a91852b1e44045ead3d20ccd5db4cf
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Sep 28 01:59:02 2017 +0000

    Fix nearbyint arithmetic moved before feholdexcept (bug 22225).
    
    In <https://sourceware.org/ml/libc-alpha/2013-05/msg00722.html> I
    remarked on the possibility of arithmetic in various nearbyint
    implementations being scheduled before feholdexcept calls, resulting
    in spurious "inexact" exceptions.
    
    I'm now actually observing this occurring in glibc built for ARM with
    GCC 7 (in fact, both copies of the same addition/subtraction sequence
    being combined and moved out before the conditionals and
    feholdexcept/fesetenv pairs), resulting in test failures.
    
    This patch makes the nearbyint implementations with this particular
    feholdexcept / arithmetic / fesetenv pattern consistently use
    math_opt_barrier on the function argument when first used in
    arithmetic, and also consistently use math_force_eval before fesetenv
    (the latter was generally already done, but the dbl-64/wordsize-64
    implementation used math_opt_barrier instead, and as
    math_opt_barrier's intended effect is through its output value being
    used, such a use that doesn't use the return value is suspect).
    
    Tested for x86_64 (--disable-multi-arch so more of these
    implementations get used), and for ARM in a configuration where I saw
    the problem scheduling.
    
    	[BZ #22225]
    	* sysdeps/ieee754/dbl-64/s_nearbyint.c (__nearbyint): Use
    	math_opt_barrier on argument when doing arithmetic on it.
    	* sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c (__nearbyint):
    	Likewise.  Use math_force_eval not math_opt_barrier after
    	arithmetic.
    	* sysdeps/ieee754/flt-32/s_nearbyintf.c (__nearbyintf): Use
    	math_opt_barrier on argument when doing arithmetic on it.
    	* sysdeps/ieee754/ldbl-128/s_nearbyintl.c (__nearbyintl):
    	Likewise.
    
    (cherry picked from commit f124cb381116b5809de198327690ad0bd8d1478e)

diff --git a/ChangeLog b/ChangeLog
index 382674d..992722a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2017-09-28  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #22225]
+	* sysdeps/ieee754/dbl-64/s_nearbyint.c (__nearbyint): Use
+	math_opt_barrier on argument when doing arithmetic on it.
+	* sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c (__nearbyint):
+	Likewise.  Use math_force_eval not math_opt_barrier after
+	arithmetic.
+	* sysdeps/ieee754/flt-32/s_nearbyintf.c (__nearbyintf): Use
+	math_opt_barrier on argument when doing arithmetic on it.
+	* sysdeps/ieee754/ldbl-128/s_nearbyintl.c (__nearbyintl):
+	Likewise.
+
 2017-09-22  Gabriel F. T. Gomes  <gabriel@inconstante.eti.br>
 
 	[BZ #22146]
diff --git a/sysdeps/ieee754/dbl-64/s_nearbyint.c b/sysdeps/ieee754/dbl-64/s_nearbyint.c
index dec0c5d..6e3f831 100644
--- a/sysdeps/ieee754/dbl-64/s_nearbyint.c
+++ b/sysdeps/ieee754/dbl-64/s_nearbyint.c
@@ -48,7 +48,7 @@ __nearbyint (double x)
       if (j0 < 0)
 	{
 	  libc_feholdexcept (&env);
-	  w = TWO52[sx] + x;
+	  w = TWO52[sx] + math_opt_barrier (x);
 	  t = w - TWO52[sx];
 	  math_force_eval (t);
 	  libc_fesetenv (&env);
@@ -65,7 +65,7 @@ __nearbyint (double x)
 	return x;                       /* x is integral */
     }
   libc_feholdexcept (&env);
-  w = TWO52[sx] + x;
+  w = TWO52[sx] + math_opt_barrier (x);
   t = w - TWO52[sx];
   math_force_eval (t);
   libc_fesetenv (&env);
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c
index 8293819..7d135b5 100644
--- a/sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c
@@ -42,9 +42,9 @@ __nearbyint(double x)
 	if(__builtin_expect(j0<52, 1)) {
 	    if(j0<0) {
 		libc_feholdexcept (&env);
-		double w = TWO52[sx]+x;
+		double w = TWO52[sx] + math_opt_barrier (x);
 		double t =  w-TWO52[sx];
-		math_opt_barrier(t);
+		math_force_eval (t);
 		libc_fesetenv (&env);
 		return __copysign (t, x);
 	    }
@@ -53,9 +53,9 @@ __nearbyint(double x)
 	    else return x;		/* x is integral */
 	}
 	libc_feholdexcept (&env);
-	double w = TWO52[sx]+x;
+	double w = TWO52[sx] + math_opt_barrier (x);
 	double t = w-TWO52[sx];
-	math_opt_barrier (t);
+	math_force_eval (t);
 	libc_fesetenv (&env);
 	return t;
 }
diff --git a/sysdeps/ieee754/flt-32/s_nearbyintf.c b/sysdeps/ieee754/flt-32/s_nearbyintf.c
index 5aebefa..b06df6b 100644
--- a/sysdeps/ieee754/flt-32/s_nearbyintf.c
+++ b/sysdeps/ieee754/flt-32/s_nearbyintf.c
@@ -37,7 +37,7 @@ __nearbyintf(float x)
 	if(j0<23) {
 	    if(j0<0) {
 		libc_feholdexceptf (&env);
-		w = TWO23[sx]+x;
+		w = TWO23[sx] + math_opt_barrier (x);
 		t =  w-TWO23[sx];
 		math_force_eval (t);
 		libc_fesetenvf (&env);
@@ -50,7 +50,7 @@ __nearbyintf(float x)
 	    else return x;		/* x is integral */
 	}
 	libc_feholdexceptf (&env);
-	w = TWO23[sx]+x;
+	w = TWO23[sx] + math_opt_barrier (x);
 	t = w-TWO23[sx];
 	math_force_eval (t);
 	libc_fesetenvf (&env);
diff --git a/sysdeps/ieee754/ldbl-128/s_nearbyintl.c b/sysdeps/ieee754/ldbl-128/s_nearbyintl.c
index 1565a81..98a33d2 100644
--- a/sysdeps/ieee754/ldbl-128/s_nearbyintl.c
+++ b/sysdeps/ieee754/ldbl-128/s_nearbyintl.c
@@ -45,7 +45,7 @@ _Float128 __nearbyintl(_Float128 x)
 	if(j0<112) {
 	    if(j0<0) {
 		feholdexcept (&env);
-	        w = TWO112[sx]+x;
+	        w = TWO112[sx] + math_opt_barrier (x);
 	        t = w-TWO112[sx];
 		math_force_eval (t);
 	        fesetenv (&env);
@@ -58,7 +58,7 @@ _Float128 __nearbyintl(_Float128 x)
 	    else return x;		/* x is integral */
 	}
 	feholdexcept (&env);
-	w = TWO112[sx]+x;
+	w = TWO112[sx] + math_opt_barrier (x);
 	t = w-TWO112[sx];
 	math_force_eval (t);
 	fesetenv (&env);

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                        |   13 +++++++++++++
 sysdeps/ieee754/dbl-64/s_nearbyint.c             |    4 ++--
 sysdeps/ieee754/dbl-64/wordsize-64/s_nearbyint.c |    8 ++++----
 sysdeps/ieee754/flt-32/s_nearbyintf.c            |    4 ++--
 sysdeps/ieee754/ldbl-128/s_nearbyintl.c          |    4 ++--
 5 files changed, 23 insertions(+), 10 deletions(-)


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