rtl combine should consider NaNs when generate fp min/max [PR94708]

    As discussed on PR94708, it's unsafe for rtl combine to generate fp
    min/max under -funsafe-math-optimizations, considering NaNs. In
    addition to flag_unsafe_math_optimizations check, we also need to
    do extra mode feature testing here: && !HONOR_NANS (mode)
    && !HONOR_SIGNED_ZEROS (mode)

    2020-04-24  Haijian Zhang <z.zhanghaijian@huawei.com>

    gcc/
	PR rtl-optimization/94708
	* combine.c (simplify_if_then_else): Add check for
	!HONOR_NANS (mode) && !HONOR_SIGNED_ZEROS (mode).
    gcc/testsuite/
	PR fortran/94708
	* gfortran.dg/pr94708.f90: New test.

gcc/ChangeLog

+2020-04-24  Haijian Zhang <z.zhanghaijian@huawei.com>
+
+	PR rtl-optimization/94708
+	* combine.c (simplify_if_then_else): Add check for
+	!HONOR_NANS (mode) && !HONOR_SIGNED_ZEROS (mode).
+
 2020-04-23  Martin Sebor  <msebor@redhat.com>
 
 	PR driver/90983

gcc/combine.c

@@ -6643,7 +6643,10 @@ simplify_if_then_else (rtx x)
 
   /* Look for MIN or MAX.  */
 
-  if ((! FLOAT_MODE_P (mode) || flag_unsafe_math_optimizations)
+  if ((! FLOAT_MODE_P (mode)
+       || (flag_unsafe_math_optimizations
+	   && !HONOR_NANS (mode)
+	   && !HONOR_SIGNED_ZEROS (mode)))
       && comparison_p
       && rtx_equal_p (XEXP (cond, 0), true_rtx)
       && rtx_equal_p (XEXP (cond, 1), false_rtx)

gcc/testsuite/ChangeLog

+2020-04-24  Haijian Zhang <z.zhanghaijian@huawei.com>
+
+	PR rtl-optimization/94708
+	* gfortran.dg/pr94708.f90: New test.
+
 2020-04-23  David Edelsohn  <dje.gcc@gmail.com>
 
 	* gcc.dg/torture/pr90020.c: Skip on AIX.

gcc/testsuite/gfortran.dg/pr94708.f90

+! { dg-do compile { target aarch64*-*-* } }
+! { dg-options "-O2 -funsafe-math-optimizations -fdump-rtl-combine" }
+
+subroutine f(vara,varb,varc,res)
+      REAL, INTENT(IN) :: vara,varb,varc
+      REAL, INTENT(out) :: res
+
+      res = vara
+      if (res .lt. varb)  res = varb
+      if (res .gt. varc)  res = varc
+end subroutine
+
+! { dg-final { scan-rtl-dump-not "smin" "combine" } }