[gcc r13-5179] [PR107608] [range-ops] Avoid folding into INF when flag_trapping_math.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:844190af178c210a6aff6b7eb4dd8c6a49210ff9

commit r13-5179-g844190af178c210a6aff6b7eb4dd8c6a49210ff9
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Tue Jan 10 10:57:16 2023 +0100

    [PR107608] [range-ops] Avoid folding into INF when flag_trapping_math.
    
    As discussed in the PR, for trapping math, do not fold overflowing
    operations into +-INF as doing so could elide a trap.
    
    There is a minor adjustment to known_isinf() where it was mistakenly
    returning true for an [infinity U NAN], whereas it should only return
    true when the range is exclusively +INF or -INF.  This is benign, as
    there were no users of known_isinf up to now.
    
    Tested on x86-64 Linux.
    
    I also ran the glibc testsuite (git sources) on x86-64 and this patch
    fixes:
    
    -FAIL: math/test-double-lgamma
    -FAIL: math/test-double-log1p
    -FAIL: math/test-float-lgamma
    -FAIL: math/test-float-log1p
    -FAIL: math/test-float128-catan
    -FAIL: math/test-float128-catanh
    -FAIL: math/test-float128-lgamma
    -FAIL: math/test-float128-log
    -FAIL: math/test-float128-log1p
    -FAIL: math/test-float128-y0
    -FAIL: math/test-float128-y1
    -FAIL: math/test-float32-lgamma
    -FAIL: math/test-float32-log1p
    -FAIL: math/test-float32x-lgamma
    -FAIL: math/test-float32x-log1p
    -FAIL: math/test-float64-lgamma
    -FAIL: math/test-float64-log1p
    -FAIL: math/test-float64x-lgamma
    -FAIL: math/test-ldouble-lgamma
    
            PR tree-optimization/107608
    
    gcc/ChangeLog:
    
            * range-op-float.cc (range_operator_float::fold_range): Avoid
            folding into INF when flag_trapping_math.
            * value-range.h (frange::known_isinf): Return false for possible NANs.

Diff:
---
 gcc/range-op-float.cc | 21 +++++++++++++++++++++
 gcc/value-range.h     |  1 +
 2 files changed, 22 insertions(+)

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 986a3896a4f..74ac4658378 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -91,6 +91,27 @@ range_operator_float::fold_range (frange &r, tree type,
   else
     r.clear_nan ();
 
+  // If the result has overflowed and flag_trapping_math, folding this
+  // operation could elide an overflow or division by zero exception.
+  // Avoid returning a singleton +-INF, to keep the propagators (DOM
+  // and substitute_and_fold_engine) from folding.  See PR107608.
+  if (flag_trapping_math
+      && MODE_HAS_INFINITIES (TYPE_MODE (type))
+      && r.known_isinf () && !op1.known_isinf () && !op2.known_isinf ())
+    {
+      REAL_VALUE_TYPE inf = r.lower_bound ();
+      if (real_isneg (&inf))
+	{
+	  REAL_VALUE_TYPE min = real_min_representable (type);
+	  r.set (type, inf, min);
+	}
+      else
+	{
+	  REAL_VALUE_TYPE max = real_max_representable (type);
+	  r.set (type, max, inf);
+	}
+    }
+
   return true;
 }
 
diff --git a/gcc/value-range.h b/gcc/value-range.h
index ea50ed3e64a..f4ac73b499f 100644
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -1300,6 +1300,7 @@ inline bool
 frange::known_isinf () const
 {
   return (m_kind == VR_RANGE
+	  && !maybe_isnan ()
 	  && real_identical (&m_min, &m_max)
 	  && real_isinf (&m_min));
 }