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

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, MIPS, MIPS64
with -O, -O1, -Os.
For AARCH64 it needs one more fix in locale for -Os:
https://sourceware.org/ml/libc-alpha/2018-09/msg00539.html

	[BZ #19444]
	* sysdeps/ieee754/dbl-64/e_jn.c (__ieee754_jn): Use
	__builtin_unreachable for default case in switch.
	(__ieee754_yn): Likewise.
	* sysdeps/ieee754/ldbl-96/e_jnl.c (__ieee754_jnl): Likewise.
	(__ieee754_ynl): Likewise.
	* sysdeps/ieee754/ldbl-128/e_jnl.c (__ieee754_jnl): Likewise.
	(__ieee754_ynl): Likewise.
	* sysdeps/ieee754/ldbl-128ibm/e_jnl.c (__ieee754_jnl): Likewise.
	(__ieee754_ynl): Likewise.

4 files changed, 14 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/e_jn.c b/sysdeps/ieee754/dbl-64/e_jn.c
index aff06ead16..90a7e77270 100644
--- a/sysdeps/ieee754/dbl-64/e_jn.c
+++ b/sysdeps/ieee754/dbl-64/e_jn.c
@@ -109,6 +109,7 @@ __ieee754_jn (int n, double x)
 	      case 1: temp = -c + s; break;
 	      case 2: temp = -c - s; break;
 	      case 3: temp = c - s; break;
+	      default: __builtin_unreachable ();
 	      }
 	    b = invsqrtpi * temp / sqrt (x);
 	  }
@@ -316,6 +317,7 @@ __ieee754_yn (int n, double x)
 	  case 1: temp = -s - c; break;
 	  case 2: temp = -s + c; break;
 	  case 3: temp = s + c; break;
+	  default: __builtin_unreachable ();
 	  }
 	b = invsqrtpi * temp / sqrt (x);
       }
diff --git a/sysdeps/ieee754/ldbl-128/e_jnl.c b/sysdeps/ieee754/ldbl-128/e_jnl.c
index 7610d18c67..3c90072a22 100644
--- a/sysdeps/ieee754/ldbl-128/e_jnl.c
+++ b/sysdeps/ieee754/ldbl-128/e_jnl.c
@@ -150,6 +150,8 @@ __ieee754_jnl (int n, _Float128 x)
 	      case 3:
 		temp = c - s;
 		break;
+	      default:
+		__builtin_unreachable ();
 	      }
 	    b = invsqrtpi * temp / sqrtl (x);
 	  }
@@ -386,6 +388,8 @@ __ieee754_ynl (int n, _Float128 x)
 	  case 3:
 	    temp = s + c;
 	    break;
+	  default:
+	    __builtin_unreachable ();
 	  }
 	b = invsqrtpi * temp / sqrtl (x);
       }
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_jnl.c b/sysdeps/ieee754/ldbl-128ibm/e_jnl.c
index 50b4558e74..478824c8fa 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_jnl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_jnl.c
@@ -150,6 +150,8 @@ __ieee754_jnl (int n, long double x)
 	      case 3:
 		temp = c - s;
 		break;
+	      default:
+		__builtin_unreachable ();
 	      }
 	    b = invsqrtpi * temp / sqrtl (x);
 	  }
@@ -386,6 +388,8 @@ __ieee754_ynl (int n, long double x)
 	  case 3:
 	    temp = s + c;
 	    break;
+	  default:
+	    __builtin_unreachable ();
 	  }
 	b = invsqrtpi * temp / sqrtl (x);
       }
diff --git a/sysdeps/ieee754/ldbl-96/e_jnl.c b/sysdeps/ieee754/ldbl-96/e_jnl.c
index 855190841b..6c1c4b4653 100644
--- a/sysdeps/ieee754/ldbl-96/e_jnl.c
+++ b/sysdeps/ieee754/ldbl-96/e_jnl.c
@@ -143,6 +143,8 @@ __ieee754_jnl (int n, long double x)
 	      case 3:
 		temp = c - s;
 		break;
+	      default:
+		__builtin_unreachable ();
 	      }
 	    b = invsqrtpi * temp / sqrtl (x);
 	  }
@@ -372,6 +374,8 @@ __ieee754_ynl (int n, long double x)
 	  case 3:
 	    temp = s + c;
 	    break;
+	  default:
+	    __builtin_unreachable ();
 	  }
 	b = invsqrtpi * temp / sqrtl (x);
       }