[gcc r13-4877] tree-ssa-dom: can_infer_simple_equiv fixes [PR108068]

[gcc r13-4877] tree-ssa-dom: can_infer_simple_equiv fixes [PR108068]

[Jakub Jelinek]

https://gcc.gnu.org/g:fd1b0aefda5b65f3f841ca6e61ccea6a72daa060

commit r13-4877-gfd1b0aefda5b65f3f841ca6e61ccea6a72daa060
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Dec 23 16:12:21 2022 +0100

    tree-ssa-dom: can_infer_simple_equiv fixes [PR108068]
    
    As reported in the PR, tree-ssa-dom.cc uses real_zerop call to find
    if a floating point constant is zero and it shouldn't try to infer
    equivalences from comparison against it if signed zeros are honored.
    This doesn't work at all for decimal types, because real_zerop always
    returns false for them (one can have different representations of decimal
    zero beyond -0/+0), and it doesn't work for vector compares either,
    as real_zerop checks if all elements are zero, while we need to avoid
    infering equivalences from comparison against vector constants which have
    at least one zero element in it (if signed zeros are honored).
    Furthermore, as mentioned by Joseph, for decimal types many other values
    aren't singleton.
    
    So, this patch stops infering anything if element mode is decimal, and
    otherwise uses instead of real_zerop a new function, real_maybe_zerop,
    which will work even for decimal types and for complex or vector will
    return true if any element is or might be zero (so it returns true
    for anything but constants for now).
    
    2022-12-23  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/108068
            * tree.h (real_maybe_zerop): Declare.
            * tree.cc (real_maybe_zerop): Define.
            * tree-ssa-dom.cc (record_edge_info): Use it instead of
            real_zerop or TREE_CODE (op1) == SSA_NAME || real_zerop.  Always set
            can_infer_simple_equiv to false for decimal floating point types.
    
            * gcc.dg/dfp/pr108068.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/dfp/pr108068.c | 14 ++++++++++++++
 gcc/tree-ssa-dom.cc                 | 12 ++++++------
 gcc/tree.cc                         | 29 +++++++++++++++++++++++++++++
 gcc/tree.h                          |  1 +
 4 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/dfp/pr108068.c b/gcc/testsuite/gcc.dg/dfp/pr108068.c
new file mode 100644
index 00000000000..6cbb0fbe602
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/dfp/pr108068.c
@@ -0,0 +1,14 @@
+/* PR tree-optimization/108068 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+int
+main ()
+{
+  _Decimal64 x = -1;
+  while (x != 0)
+    x /= 10;
+  double d = x;
+  if (!__builtin_signbit (d))
+    __builtin_abort ();
+}
diff --git a/gcc/tree-ssa-dom.cc b/gcc/tree-ssa-dom.cc
index c9e52d1ee94..76834fdbef4 100644
--- a/gcc/tree-ssa-dom.cc
+++ b/gcc/tree-ssa-dom.cc
@@ -615,9 +615,9 @@ record_edge_info (basic_block bb)
             {
               tree cond = build2 (code, boolean_type_node, op0, op1);
               tree inverted = invert_truthvalue_loc (loc, cond);
-              bool can_infer_simple_equiv
-                = !(HONOR_SIGNED_ZEROS (op0)
-                    && real_zerop (op0));
+	      bool can_infer_simple_equiv
+		= !(HONOR_SIGNED_ZEROS (op0) && real_maybe_zerop (op0))
+		  && !DECIMAL_FLOAT_MODE_P (element_mode (TREE_TYPE (op0)));
 	      class edge_info *edge_info;
 
 	      edge_info = new class edge_info (true_edge);
@@ -639,9 +639,9 @@ record_edge_info (basic_block bb)
             {
               tree cond = build2 (code, boolean_type_node, op0, op1);
               tree inverted = invert_truthvalue_loc (loc, cond);
-              bool can_infer_simple_equiv
-                = !(HONOR_SIGNED_ZEROS (op1)
-                    && (TREE_CODE (op1) == SSA_NAME || real_zerop (op1)));
+	      bool can_infer_simple_equiv
+		= !(HONOR_SIGNED_ZEROS (op1) && real_maybe_zerop (op1))
+		  && !DECIMAL_FLOAT_MODE_P (element_mode (TREE_TYPE (op1)));
 	      class edge_info *edge_info;
 
 	      edge_info = new class edge_info (true_edge);
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 581d4489438..6b3273e8997 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -3180,6 +3180,35 @@ real_minus_onep (const_tree expr)
     }
 }
 
+/* Return true if T could be a floating point zero.  */
+
+bool
+real_maybe_zerop (const_tree expr)
+{
+  switch (TREE_CODE (expr))
+    {
+    case REAL_CST:
+      /* Can't use real_zerop here, as it always returns false for decimal
+	 floats.  And can't use TREE_REAL_CST (expr).cl == rvc_zero
+	 either, as decimal zeros are rvc_normal.  */
+      return real_equal (&TREE_REAL_CST (expr), &dconst0);
+    case COMPLEX_CST:
+      return (real_maybe_zerop (TREE_REALPART (expr))
+	      || real_maybe_zerop (TREE_IMAGPART (expr)));
+    case VECTOR_CST:
+      {
+	unsigned count = vector_cst_encoded_nelts (expr);
+	for (unsigned int i = 0; i < count; ++i)
+	  if (real_maybe_zerop (VECTOR_CST_ENCODED_ELT (expr, i)))
+	    return true;
+	return false;
+      }
+    default:
+      /* Perhaps for SSA_NAMEs we could query frange.  */
+      return true;
+    }
+}
+
 /* Nonzero if EXP is a constant or a cast of a constant.  */
 
 bool
diff --git a/gcc/tree.h b/gcc/tree.h
index 64a241f51e2..7e26e726bc5 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -5497,6 +5497,7 @@ extern bool needs_to_live_in_memory (const_tree);
 extern tree reconstruct_complex_type (tree, tree);
 extern bool real_onep (const_tree);
 extern bool real_minus_onep (const_tree);
+extern bool real_maybe_zerop (const_tree);
 extern void init_ttree (void);
 extern void build_common_tree_nodes (bool);
 extern void build_common_builtin_nodes (void);