Re: [PATCH] Handle > INF and < INF correctly in range-op-float.cc

[Aldy Hernandez <aldyh@redhat.com>]

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On Tue, Sep 6, 2022 at 9:59 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Tue, Sep 06, 2022 at 09:49:55AM +0200, Aldy Hernandez wrote:
> > On Tue, Sep 6, 2022 at 9:44 AM Jakub Jelinek <jakub@redhat.com> wrote:
> > >
> > > On Tue, Sep 06, 2022 at 09:40:59AM +0200, Aldy Hernandez wrote:
> > > > if (x <= Inf)
> > >
> > > This will be [-Inf, Inf] !NAN on the true side and
> > > NAN (either sign) on the false side indeed.
> > >
> > > > if (x < -Inf)
> > >
> > > will be NAN (either sign) on the true side and
> > > [-Inf, Inf] !NAN on the false side.
> >
> > Sweet, that's exactly what I thought, thus the patch.
> >
> > Furthermore, for !HONOR_NANS I would expect the NAN sides above to be
> > UNDEFINED/unreachable.  That is, the false side of x <= Inf when
> > !HONOR_NANS is unreachable.
>
> In practice, there is no real format that has NaNs and doesn't have Infs
> or vice versa and similarly we have just one switch to cover both Infinities
> and NaNs, so either both are supported, or neither of them, or both
> are supported but neither of them should appear in a valid program
> (-ffinite-math-only on most floating point formats).
> So the answer in that case is a little bit fuzzy because one shouldn't
> compare against infinity in that case (or for !MODE_HAS_INFINITIES even
> can't).  But sure, if NaNs aren't possible or can't appear and you compare
> x <= Largest_possible_float, then it is always true and so UNDEFINED on the
> false edge.

OK, let's leave it as undefined to be consistent.

Come to think of it, perhaps we could represent the endpoints
(varying, [x, +INF], etc) as the min/max representable values for the
type (for !HONOR_NANS).  I don't think it would make a big difference,
but we might get better results for some corner cases.

Question...for !HONOR_NANS or !HONOR_INFINITIES or whatever, say the
range for the domain is [-MIN, +MAX] for the min and max representable
numbers.  What happens for MAX+1?  Is that undefined?  I wonder what
real.cc does for that.

Attached is the final version of the patch I'm pushing.  Tested (+mpfr
tests) on x86-64 Linux.

Aldy

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From fd52ffb9997becafa31c5109b50fe274da12aed8 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Tue, 6 Sep 2022 08:20:54 +0200
Subject: [PATCH] Handle > INF and < INF correctly in range-op-float.cc

The gfortran.dg/minlocval*.f90 tests are generating conditionals past
the infinities.  For example:

	if (x <= +Inf)
	  foo (x);
	else
	  bar (x);

It seems to me that the only possible value for x on the false side is
either NAN or undefined (for !HONOR_NANS).

gcc/ChangeLog:

	* range-op-float.cc (build_le): Handle NANs and going past infinity.
	(build_lt): Same.
	(build_ge): Same.
	(build_gt): Same.
	(foperator_lt::op1_range): Avoid adjustments to range if build_*
	returned false.
	(foperator_lt::op2_range): Same.
	(foperator_le::op1_range): Same.
	(foperator_le::op2_range): Same.
	(foperator_gt::op1_range): Same.
	(foperator_gt::op2_range): Same.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/vrp-float-inf-1.c: New test.
---
 gcc/range-op-float.cc                         | 99 ++++++++++++++-----
 .../gcc.dg/tree-ssa/vrp-float-inf-1.c         | 15 +++
 2 files changed, 90 insertions(+), 24 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/vrp-float-inf-1.c

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 050f07a9867..5fbbaa1fb36 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -224,36 +224,79 @@ frange_drop_ninf (frange &r, tree type)
 
 // (X <= VAL) produces the range of [-INF, VAL].
 
-static void
+static bool
 build_le (frange &r, tree type, const REAL_VALUE_TYPE &val)
 {
+  if (real_isnan (&val))
+    {
+      r.set_undefined ();
+      return false;
+    }
   r.set (type, dconstninf, val);
+  return true;
 }
 
 // (X < VAL) produces the range of [-INF, VAL).
 
-static void
+static bool
 build_lt (frange &r, tree type, const REAL_VALUE_TYPE &val)
 {
+  if (real_isnan (&val))
+    {
+      r.set_undefined ();
+      return false;
+    }
+  // < -INF is outside the range.
+  if (real_isinf (&val, 1))
+    {
+      if (HONOR_NANS (type))
+	frange_set_nan (r, type);
+      else
+	r.set_undefined ();
+      return false;
+    }
   // Hijack LE because we only support closed intervals.
   build_le (r, type, val);
+  return true;
 }
 
 // (X >= VAL) produces the range of [VAL, +INF].
 
-static void
+static bool
 build_ge (frange &r, tree type, const REAL_VALUE_TYPE &val)
 {
+  if (real_isnan (&val))
+    {
+      r.set_undefined ();
+      return false;
+    }
   r.set (type, val, dconstinf);
+  return true;
 }
 
 // (X > VAL) produces the range of (VAL, +INF].
 
-static void
+static bool
 build_gt (frange &r, tree type, const REAL_VALUE_TYPE &val)
 {
+  if (real_isnan (&val))
+    {
+      r.set_undefined ();
+      return false;
+    }
+  // > +INF is outside the range.
+  if (real_isinf (&val, 0))
+    {
+      if (HONOR_NANS (type))
+	frange_set_nan (r, type);
+      else
+	r.set_undefined ();
+      return false;
+    }
+
   // Hijack GE because we only support closed intervals.
   build_ge (r, type, val);
+  return true;
 }
 
 
@@ -520,10 +563,12 @@ foperator_lt::op1_range (frange &r,
   switch (get_bool_state (r, lhs, type))
     {
     case BRS_TRUE:
-      build_lt (r, type, op2.upper_bound ());
-      r.set_nan (fp_prop::NO);
-      // x < y implies x is not +INF.
-      frange_drop_inf (r, type);
+      if (build_lt (r, type, op2.upper_bound ()))
+	{
+	  r.set_nan (fp_prop::NO);
+	  // x < y implies x is not +INF.
+	  frange_drop_inf (r, type);
+	}
       break;
 
     case BRS_FALSE:
@@ -546,10 +591,12 @@ foperator_lt::op2_range (frange &r,
   switch (get_bool_state (r, lhs, type))
     {
     case BRS_TRUE:
-      build_gt (r, type, op1.lower_bound ());
-      r.set_nan (fp_prop::NO);
-      // x < y implies y is not -INF.
-      frange_drop_ninf (r, type);
+      if (build_gt (r, type, op1.lower_bound ()))
+	{
+	  r.set_nan (fp_prop::NO);
+	  // x < y implies y is not -INF.
+	  frange_drop_ninf (r, type);
+	}
       break;
 
     case BRS_FALSE:
@@ -618,8 +665,8 @@ foperator_le::op1_range (frange &r,
   switch (get_bool_state (r, lhs, type))
     {
     case BRS_TRUE:
-      build_le (r, type, op2.upper_bound ());
-      r.set_nan (fp_prop::NO);
+      if (build_le (r, type, op2.upper_bound ()))
+	r.set_nan (fp_prop::NO);
       break;
 
     case BRS_FALSE:
@@ -642,8 +689,8 @@ foperator_le::op2_range (frange &r,
   switch (get_bool_state (r, lhs, type))
     {
     case BRS_TRUE:
-      build_ge (r, type, op1.lower_bound ());
-      r.set_nan (fp_prop::NO);
+      if (build_ge (r, type, op1.lower_bound ()))
+	r.set_nan (fp_prop::NO);
       break;
 
     case BRS_FALSE:
@@ -712,10 +759,12 @@ foperator_gt::op1_range (frange &r,
   switch (get_bool_state (r, lhs, type))
     {
     case BRS_TRUE:
-      build_gt (r, type, op2.lower_bound ());
-      r.set_nan (fp_prop::NO);
-      // x > y implies x is not -INF.
-      frange_drop_ninf (r, type);
+      if (build_gt (r, type, op2.lower_bound ()))
+	{
+	  r.set_nan (fp_prop::NO);
+	  // x > y implies x is not -INF.
+	  frange_drop_ninf (r, type);
+	}
       break;
 
     case BRS_FALSE:
@@ -738,10 +787,12 @@ foperator_gt::op2_range (frange &r,
   switch (get_bool_state (r, lhs, type))
     {
     case BRS_TRUE:
-      build_lt (r, type, op1.upper_bound ());
-      r.set_nan (fp_prop::NO);
-      // x > y implies y is not +INF.
-      frange_drop_inf (r, type);
+      if (build_lt (r, type, op1.upper_bound ()))
+	{
+	  r.set_nan (fp_prop::NO);
+	  // x > y implies y is not +INF.
+	  frange_drop_inf (r, type);
+	}
       break;
 
     case BRS_FALSE:
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-inf-1.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-inf-1.c
new file mode 100644
index 00000000000..1d21cce41e6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-inf-1.c
@@ -0,0 +1,15 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-evrp-details" }
+
+void foo ();
+void bar (double);
+
+void funky(double f, double g)
+{
+  if (f <= __builtin_inf ())
+    foo ();
+  else
+    bar (f);
+}
+
+// { dg-final { scan-tree-dump-not " Inf,  Inf" "evrp" } }
-- 
2.37.1