Fix folding of Inf/NaN comparisons for -ftrapping-math (PR tree-optimization/64811)

[Joseph Myers]

The folding of comparisons against Inf (to constants or comparisons
with the maximum finite value) has various cases where it introduces
or loses "invalid" exceptions for comparisons with NaNs.

Folding x > +Inf to 0 should not be about HONOR_SNANS - ordered
comparisons of both quiet and signaling NaNs should raise invalid.

x <= +Inf is not the same as x == x, because again that loses an
exception (equality comparisons don't raise exceptions except for
signaling NaNs).

x == +Inf is not the same as x > DBL_MAX, and a similar issue applies
with the x != +Inf case - that transformation causes a spurious
exception.

This patch fixes the conditionals on the folding to avoid such
introducing or losing exceptions.

Bootstrapped with no regressions on x86_64-pc-linux-gnu (where the
cases involving spurious exceptions wouldn't have failed anyway before
GCC 8 because of unordered comparisons wrongly always having formerly
been used by the back end).  Also tested for powerpc-linux-gnu
soft-float that this fixes many glibc math/ test failures that arose
in that configuration because this folding affected the IBM long
double support in libgcc (no such failures appeared for hard-float
because of the bug of powerpc hard-float always using unordered
comparisons) - some failures remain, but I believe them to be
unrelated.  OK to commit?

gcc:
2018-01-05  Joseph Myers  <joseph@codesourcery.com>

	PR tree-optimization/64811
	* match.pd: When optimizing comparisons with Inf, avoid
	introducing or losing exceptions from comparisons with NaN.

gcc/testsuite:
2018-01-05  Joseph Myers  <joseph@codesourcery.com>

	PR tree-optimization/64811
	* gcc.dg/torture/inf-compare-1.c, gcc.dg/torture/inf-compare-2.c,
	gcc.dg/torture/inf-compare-3.c, gcc.dg/torture/inf-compare-4.c,
	gcc.dg/torture/inf-compare-5.c, gcc.dg/torture/inf-compare-6.c,
	gcc.dg/torture/inf-compare-7.c, gcc.dg/torture/inf-compare-8.c:
	New tests.
	* gcc.c-torture/execute/ieee/fp-cmp-7.x: New file.

Index: gcc/match.pd
===================================================================
--- gcc/match.pd	(revision 256279)
+++ gcc/match.pd	(working copy)
@@ -3050,18 +3050,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
          code = swap_tree_comparison (code);
      }
      (switch
-      /* x > +Inf is always false, if with ignore sNANs.  */
+      /* x > +Inf is always false, if we ignore NaNs or exceptions.  */
       (if (code == GT_EXPR
-	   && ! HONOR_SNANS (@0))
+	   && !(HONOR_NANS (@0) && flag_trapping_math))
        { constant_boolean_node (false, type); })
       (if (code == LE_EXPR)
-       /* x <= +Inf is always true, if we don't case about NaNs.  */
+       /* x <= +Inf is always true, if we don't care about NaNs.  */
        (if (! HONOR_NANS (@0))
 	{ constant_boolean_node (true, type); }
-	/* x <= +Inf is the same as x == x, i.e. !isnan(x).  */
-	(eq @0 @0)))
-      /* x == +Inf and x >= +Inf are always equal to x > DBL_MAX.  */
-      (if (code == EQ_EXPR || code == GE_EXPR)
+	/* x <= +Inf is the same as x == x, i.e. !isnan(x), but this loses
+	   an "invalid" exception.  */
+	(if (!flag_trapping_math)
+	 (eq @0 @0))))
+      /* x == +Inf and x >= +Inf are always equal to x > DBL_MAX, but
+	 for == this introduces an exception for x a NaN.  */
+      (if ((code == EQ_EXPR && !(HONOR_NANS (@0) && flag_trapping_math))
+	   || code == GE_EXPR)
        (with { real_maxval (&max, neg, TYPE_MODE (TREE_TYPE (@0))); }
 	(if (neg)
 	 (lt @0 { build_real (TREE_TYPE (@0), max); })
@@ -3072,7 +3076,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	(if (neg)
 	 (ge @0 { build_real (TREE_TYPE (@0), max); })
 	 (le @0 { build_real (TREE_TYPE (@0), max); }))))
-      /* x != +Inf is always equal to !(x > DBL_MAX).  */
+      /* x != +Inf is always equal to !(x > DBL_MAX), but this introduces
+	 an exception for x a NaN so use an unordered comparison.  */
       (if (code == NE_EXPR)
        (with { real_maxval (&max, neg, TYPE_MODE (TREE_TYPE (@0))); }
 	(if (! HONOR_NANS (@0))
@@ -3080,10 +3085,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	  (ge @0 { build_real (TREE_TYPE (@0), max); })
 	  (le @0 { build_real (TREE_TYPE (@0), max); }))
 	 (if (neg)
-	  (bit_xor (lt @0 { build_real (TREE_TYPE (@0), max); })
-	   { build_one_cst (type); })
-	  (bit_xor (gt @0 { build_real (TREE_TYPE (@0), max); })
-	   { build_one_cst (type); }))))))))))
+	  (unge @0 { build_real (TREE_TYPE (@0), max); })
+	  (unle @0 { build_real (TREE_TYPE (@0), max); }))))))))))
 
  /* If this is a comparison of a real constant with a PLUS_EXPR
     or a MINUS_EXPR of a real constant, we can convert it into a
Index: gcc/testsuite/gcc.c-torture/execute/ieee/fp-cmp-7.x
===================================================================
--- gcc/testsuite/gcc.c-torture/execute/ieee/fp-cmp-7.x	(nonexistent)
+++ gcc/testsuite/gcc.c-torture/execute/ieee/fp-cmp-7.x	(working copy)
@@ -0,0 +1,2 @@
+lappend additional_flags "-fno-trapping-math"
+return 0
Index: gcc/testsuite/gcc.dg/torture/inf-compare-1.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-1.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-1.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x > __builtin_inf ();
+  if (i != 0 || !fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-2.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-2.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-2.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x < -__builtin_inf ();
+  if (i != 0 || !fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-3.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-3.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-3.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x <= __builtin_inf ();
+  if (i != 0 || !fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-4.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-4.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-4.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x >= -__builtin_inf ();
+  if (i != 0 || !fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-5.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-5.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-5.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x == __builtin_inf ();
+  if (i != 0 || fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-6.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-6.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-6.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x == -__builtin_inf ();
+  if (i != 0 || fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-7.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-7.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-7.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x != __builtin_inf ();
+  if (i != 1 || fetestexcept (FE_INVALID))
+    abort ();
+}
Index: gcc/testsuite/gcc.dg/torture/inf-compare-8.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/inf-compare-8.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/inf-compare-8.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+
+extern void abort (void);
+extern void exit (int);
+
+volatile double x = __builtin_nan ("");
+volatile int i;
+
+int
+main (void)
+{
+  i = x != -__builtin_inf ();
+  if (i != 1 || fetestexcept (FE_INVALID))
+    abort ();
+}

-- 
Joseph S. Myers
joseph@codesourcery.com