rs6000: Check -+0 and NaN for smax/smin generation

PR93709 mentioned regressions on maxlocval_4.f90 and minlocval_f.f90 which
relates to max of '-inf' and 'nan'. This regression occur on P9 because
P9 new instruction 'xsmaxcdp' is generated. 
And for C code `a < b ? b : a` is also generated as `xsmaxcdp` under -O2
for P9. While this instruction behavior more like C/C++ semantic (a>b?a:b).

This generates prevents 'xsmaxcdp' to be generated for those cases.
'xsmincdp' also is handled in patch.

gcc/
2020-03-10  Jiufu Guo  <guojiufu@linux.ibm.com>

	PR target/93709
	* gcc/config/rs6000/rs6000.c (rs6000_emit_p9_fp_minmax): Check
	NAN and SIGNED_ZEROR for smax/smin.

gcc/testsuite
2020-03-10  Jiufu Guo  <guojiufu@linux.ibm.com>

	PR target/93709
	* gcc.target/powerpc/p9-minmax-3.c: New test.

gcc/ChangeLog

+2020-03-10  Jiufu Guo  <guojiufu@linux.ibm.com>
+
+	PR target/93709
+	* gcc/config/rs6000/rs6000.c (rs6000_emit_p9_fp_minmax): Check
+	NAN and SIGNED_ZEROR for smax/smin.
+
 2020-03-10  Will Schmidt  <will_schmidt@vnet.ibm.com>
 
 	PR target/90763

gcc/config/rs6000/rs6000.c

@@ -14831,7 +14831,11 @@ rs6000_emit_p9_fp_minmax (rtx dest, rtx op, rtx true_cond, rtx false_cond)
   if (rtx_equal_p (op0, true_cond) && rtx_equal_p (op1, false_cond))
     ;
 
-  else if (rtx_equal_p (op1, true_cond) && rtx_equal_p (op0, false_cond))
+  /* Only when NaNs and signed-zeros are not in effect, smax could be
+     used for `op0 < op1 ? op1 : op0`, and smin could be used for
+     `op0 > op1 ? op1 : op0`.  */
+  else if (rtx_equal_p (op1, true_cond) && rtx_equal_p (op0, false_cond)
+	   && !HONOR_NANS (compare_mode) && !HONOR_SIGNED_ZEROS (compare_mode))
     max_p = !max_p;
 
   else

gcc/testsuite/ChangeLog

+2020-03-10  Jiufu Guo  <guojiufu@linux.ibm.com>
+
+	PR target/93709
+	* gcc.target/powerpc/p9-minmax-3.c: New test.
+
 2020-03-10  Will Schmidt  <will_schmidt@vnet.ibm.com>
 
 	PR target/90763

gcc/testsuite/gcc.target/powerpc/p9-minmax-3.c

+/* { dg-do compile { target { powerpc*-*-* } } } */
+/* { dg-require-effective-target powerpc_p9vector_ok } */
+/* { dg-options "-mdejagnu-cpu=power9 -O2 -mpower9-minmax" } */
+/* { dg-final { scan-assembler-not "xsmaxcdp"   } } */
+/* { dg-final { scan-assembler-not "xsmincdp"   } } */
+
+double
+dbl_max1 (double a, double b)
+{
+  return a < b ? b : a;
+}
+
+double
+dbl_min1 (double a, double b)
+{
+  return a > b ? b : a;
+}