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[PATCHv3] sysdeps/ieee754: prevent maybe-uninitialized errors [BZ #19444]

From: Martin Jansa <martin dot jansa at gmail dot com>
To: libc-alpha at sourceware dot org
Cc: Martin Jansa <Martin dot Jansa at gmail dot com>
Date: Sat, 29 Sep 2018 19:39:07 +0000
Subject: [PATCHv3] sysdeps/ieee754: prevent maybe-uninitialized errors [BZ #19444]
References: <alpine.DEB.2.21.1809191315310.14910@digraph.polyomino.org.uk>
With -O included in CFLAGS it fails to build with:

../sysdeps/ieee754/ldbl-96/e_jnl.c: In function '__ieee754_jnl':
../sysdeps/ieee754/ldbl-96/e_jnl.c:146:20: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
      b = invsqrtpi * temp / sqrtl (x);
          ~~~~~~~~~~^~~~~~
../sysdeps/ieee754/ldbl-96/e_jnl.c: In function '__ieee754_ynl':
../sysdeps/ieee754/ldbl-96/e_jnl.c:375:16: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  b = invsqrtpi * temp / sqrtl (x);
      ~~~~~~~~~~^~~~~~
../sysdeps/ieee754/dbl-64/e_jn.c: In function '__ieee754_jn':
../sysdeps/ieee754/dbl-64/e_jn.c:113:20: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
      b = invsqrtpi * temp / sqrt (x);
          ~~~~~~~~~~^~~~~~
../sysdeps/ieee754/dbl-64/e_jn.c: In function '__ieee754_yn':
../sysdeps/ieee754/dbl-64/e_jn.c:320:16: error: 'temp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  b = invsqrtpi * temp / sqrt (x);
      ~~~~~~~~~~^~~~~~

Build tested with Yocto for ARM, AARCH64, X86, X86_64, PPC with
-O, -O1, -Os.
For soft-fp ARM it needs one more fix for -O1:
https://sourceware.org/ml/libc-alpha/2018-09/msg00300.html
For AARCH64 it needs one more fix for -Os.

        [BZ #23716]
        * sysdeps/ieee754/dbl-96/e_jnl.c: Fix build with -O
        * sysdeps/ieee754/ldbl-96/e_jnl.c: Likewise.
        * sysdeps/ieee754/ldbl-128/e_jnl.c: Likewise.
        * sysdeps/ieee754/ldbl-128ibm/e_jnl.c: Likewise.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
---
 ChangeLog                           |  7 +++++++
 sysdeps/ieee754/dbl-64/e_jn.c       | 21 +++++++++++++++++++++
 sysdeps/ieee754/ldbl-128/e_jnl.c    | 21 +++++++++++++++++++++
 sysdeps/ieee754/ldbl-128ibm/e_jnl.c | 21 +++++++++++++++++++++
 sysdeps/ieee754/ldbl-96/e_jnl.c     | 21 +++++++++++++++++++++
 5 files changed, 91 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 07760299e6..4bafeefda5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2018-09-29  Martin Jansa  <Martin.Jansa@gmail.com>
+	Partial fix for [BZ #23716]
+	* sysdeps/ieee754/dbl-96/e_jnl.c: Fix build with -O
+	* sysdeps/ieee754/ldbl-96/e_jnl.c: Likewise.
+	* sysdeps/ieee754/ldbl-128/e_jnl.c: Likewise.
+	* sysdeps/ieee754/ldbl-128ibm/e_jnl.c: Likewise.
+
 2018-09-28  Joseph Myers  <joseph@codesourcery.com>
 
 	* math/fromfp.h: Do not include <math_private.h>.
diff --git a/sysdeps/ieee754/dbl-64/e_jn.c b/sysdeps/ieee754/dbl-64/e_jn.c
index aff06ead16..20c8ff4f8f 100644
--- a/sysdeps/ieee754/dbl-64/e_jn.c
+++ b/sysdeps/ieee754/dbl-64/e_jn.c
@@ -43,6 +43,7 @@
 #include <math_private.h>
 #include <fenv_private.h>
 #include <math-underflow.h>
+#include <libc-diag.h>
 
 static const double
   invsqrtpi = 5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
@@ -110,7 +111,17 @@ __ieee754_jn (int n, double x)
 	      case 2: temp = -c - s; break;
 	      case 3: temp = c - s; break;
 	      }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	    b = invsqrtpi * temp / sqrt (x);
+DIAG_POP_NEEDS_COMMENT;
 	  }
 	else
 	  {
@@ -317,7 +328,17 @@ __ieee754_yn (int n, double x)
 	  case 2: temp = -s + c; break;
 	  case 3: temp = s + c; break;
 	  }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	b = invsqrtpi * temp / sqrt (x);
+DIAG_POP_NEEDS_COMMENT;
       }
     else
       {
diff --git a/sysdeps/ieee754/ldbl-128/e_jnl.c b/sysdeps/ieee754/ldbl-128/e_jnl.c
index 7610d18c67..fa49f72844 100644
--- a/sysdeps/ieee754/ldbl-128/e_jnl.c
+++ b/sysdeps/ieee754/ldbl-128/e_jnl.c
@@ -62,6 +62,7 @@
 #include <math_private.h>
 #include <fenv_private.h>
 #include <math-underflow.h>
+#include <libc-diag.h>
 
 static const _Float128
   invsqrtpi = L(5.6418958354775628694807945156077258584405E-1),
@@ -151,7 +152,17 @@ __ieee754_jnl (int n, _Float128 x)
 		temp = c - s;
 		break;
 	      }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	    b = invsqrtpi * temp / sqrtl (x);
+DIAG_POP_NEEDS_COMMENT;
 	  }
 	else
 	  {
@@ -387,7 +398,17 @@ __ieee754_ynl (int n, _Float128 x)
 	    temp = s + c;
 	    break;
 	  }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	b = invsqrtpi * temp / sqrtl (x);
+DIAG_POP_NEEDS_COMMENT;
       }
     else
       {
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_jnl.c b/sysdeps/ieee754/ldbl-128ibm/e_jnl.c
index 50b4558e74..1f8fd36cb8 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_jnl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_jnl.c
@@ -62,6 +62,7 @@
 #include <math_private.h>
 #include <fenv_private.h>
 #include <math-underflow.h>
+#include <libc-diag.h>
 
 static const long double
   invsqrtpi = 5.6418958354775628694807945156077258584405E-1L,
@@ -151,7 +152,17 @@ __ieee754_jnl (int n, long double x)
 		temp = c - s;
 		break;
 	      }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	    b = invsqrtpi * temp / sqrtl (x);
+DIAG_POP_NEEDS_COMMENT;
 	  }
 	else
 	  {
@@ -387,7 +398,17 @@ __ieee754_ynl (int n, long double x)
 	    temp = s + c;
 	    break;
 	  }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	b = invsqrtpi * temp / sqrtl (x);
+DIAG_POP_NEEDS_COMMENT;
       }
     else
       {
diff --git a/sysdeps/ieee754/ldbl-96/e_jnl.c b/sysdeps/ieee754/ldbl-96/e_jnl.c
index 855190841b..60964fa887 100644
--- a/sysdeps/ieee754/ldbl-96/e_jnl.c
+++ b/sysdeps/ieee754/ldbl-96/e_jnl.c
@@ -62,6 +62,7 @@
 #include <math_private.h>
 #include <fenv_private.h>
 #include <math-underflow.h>
+#include <libc-diag.h>
 
 static const long double
   invsqrtpi = 5.64189583547756286948079e-1L, two = 2.0e0L, one = 1.0e0L;
@@ -144,7 +145,17 @@ __ieee754_jnl (int n, long double x)
 		temp = c - s;
 		break;
 	      }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	    b = invsqrtpi * temp / sqrtl (x);
+DIAG_POP_NEEDS_COMMENT;
 	  }
 	else
 	  {
@@ -373,7 +384,17 @@ __ieee754_ynl (int n, long double x)
 	    temp = s + c;
 	    break;
 	  }
+/* With GCC 8 (and older) when compiling with -O the compiler
+   warns that the variable 'temp',  may be used uninitialized.
+   The switch above covers all possible values of n & 3
+   but GCC without VRP enabled isn't able to figure out the
+   range of possible values is [0,3] as explained in:
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69230
+   so it's false possitive with -O1 and lower. */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (8, "-Wmaybe-uninitialized");
 	b = invsqrtpi * temp / sqrtl (x);
+DIAG_POP_NEEDS_COMMENT;
       }
     else
       {
-- 
2.17.1
References:
- Re: [PATCH 1/2] sysdeps/ieee754: prevent maybe-uninitialized errors
  - From: Joseph Myers
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