Fix powerpc fmax, fmin sNaN handling (bug 20947).

Various fmax and fmin function implementations mishandle sNaN
arguments:

(a) When both arguments are NaNs, the return value should be a qNaN,
but sometimes it is an sNaN if at least one argument is an sNaN.

(b) Under TS 18661-1 semantics, if either argument is an sNaN then the
result should be a qNaN (whereas if one argument is a qNaN and the
other is not a NaN, the result should be the non-NaN argument).
Various implementations treat sNaNs like qNaNs here.

This patch fixes the powerpc versions of these functions (shared by
float and double, 32-bit and 64-bit).  The structure of those versions
is that all ordered cases are already handled before anything dealing
with the case where the arguments are unordered; thus, this patch
causes no change to the code executed in the common case (neither
argument a NaN).

Tested for powerpc (32-bit and 64-bit), together with tests to be
added along with the x86_64 / x86 fixes.

	[BZ #20947]
	* sysdeps/powerpc/fpu/s_fmax.S (__fmax): Add the arguments when
	either is a signaling NaN.
	* sysdeps/powerpc/fpu/s_fmin.S (__fmin): Likewise.

ChangeLog

@@ -1,3 +1,10 @@
+2016-12-15  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #20947]
+	* sysdeps/powerpc/fpu/s_fmax.S (__fmax): Add the arguments when
+	either is a signaling NaN.
+	* sysdeps/powerpc/fpu/s_fmin.S (__fmin): Likewise.
+
 2016-12-14  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #20947]

sysdeps/powerpc/fpu/s_fmax.S

@@ -25,7 +25,42 @@ ENTRY(__fmax)
 	bnulr+	cr0
 /* x and y are unordered, so one of x or y must be a NaN... */
 	fcmpu	cr1,fp2,fp2
-	bunlr	cr1
+	bun	cr1,1f
+/* x is a NaN; y is not.  Test if x is signaling.  */
+#ifdef __powerpc64__
+	stfd	fp1,-8(r1)
+	lwz	r3,-8+HIWORD(r1)
+#else
+	stwu	r1,-16(r1)
+	cfi_adjust_cfa_offset (16)
+	stfd	fp1,8(r1)
+	lwz	r3,8+HIWORD(r1)
+	addi	r1,r1,16
+	cfi_adjust_cfa_offset (-16)
+#endif
+	andis.	r3,r3,8
+	bne	cr0,0f
+	b	2f
+1:	/* y is a NaN; x may or may not be.  */
+	fcmpu	cr1,fp1,fp1
+	bun	cr1,2f
+/* y is a NaN; x is not.  Test if y is signaling.  */
+#ifdef __powerpc64__
+	stfd	fp2,-8(r1)
+	lwz	r3,-8+HIWORD(r1)
+#else
+	stwu	r1,-16(r1)
+	cfi_adjust_cfa_offset (16)
+	stfd	fp2,8(r1)
+	lwz	r3,8+HIWORD(r1)
+	addi	r1,r1,16
+	cfi_adjust_cfa_offset (-16)
+#endif
+	andis.	r3,r3,8
+	bnelr	cr0
+2:	/* x and y are NaNs, or one is a signaling NaN.  */
+	fadd	fp1,fp1,fp2
+	blr
 0:	fmr	fp1,fp2
 	blr
 END(__fmax)

sysdeps/powerpc/fpu/s_fmin.S

@@ -25,7 +25,42 @@ ENTRY(__fmin)
 	bnulr+	cr0
 /* x and y are unordered, so one of x or y must be a NaN... */
 	fcmpu	cr1,fp2,fp2
-	bunlr	cr1
+	bun	cr1,1f
+/* x is a NaN; y is not.  Test if x is signaling.  */
+#ifdef __powerpc64__
+	stfd	fp1,-8(r1)
+	lwz	r3,-8+HIWORD(r1)
+#else
+	stwu	r1,-16(r1)
+	cfi_adjust_cfa_offset (16)
+	stfd	fp1,8(r1)
+	lwz	r3,8+HIWORD(r1)
+	addi	r1,r1,16
+	cfi_adjust_cfa_offset (-16)
+#endif
+	andis.	r3,r3,8
+	bne	cr0,0f
+	b	2f
+1:	/* y is a NaN; x may or may not be.  */
+	fcmpu	cr1,fp1,fp1
+	bun	cr1,2f
+/* y is a NaN; x is not.  Test if y is signaling.  */
+#ifdef __powerpc64__
+	stfd	fp2,-8(r1)
+	lwz	r3,-8+HIWORD(r1)
+#else
+	stwu	r1,-16(r1)
+	cfi_adjust_cfa_offset (16)
+	stfd	fp2,8(r1)
+	lwz	r3,8+HIWORD(r1)
+	addi	r1,r1,16
+	cfi_adjust_cfa_offset (-16)
+#endif
+	andis.	r3,r3,8
+	bnelr	cr0
+2:	/* x and y are NaNs, or one is a signaling NaN.  */
+	fadd	fp1,fp1,fp2
+	blr
 0:	fmr	fp1,fp2
 	blr
 END(__fmin)