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[COMMITTED] PR tree-optimization/111694 - Ensure float equivalences include + and - zero.

Message ID 21d344bf-fb9f-1f0a-31ba-27626e12562a@redhat.com
State New
Headers show
Series [COMMITTED] PR tree-optimization/111694 - Ensure float equivalences include + and - zero. | expand

Commit Message

Andrew MacLeod Oct. 9, 2023, 5:10 p.m. UTC 
When ranger propagates ranges in the on-entry cache, it also check for 
equivalences and incorporates the equivalence into the range for a name 
if it is known.

With floating point values, the equivalence that is generated by 
comparison must also take into account that if the equivalence contains 
zero, both positive and negative zeros could be in the range.

This PR demonstrates that once we establish an equivalence, even though 
we know one value may only have a positive zero, the equivalence may 
have been formed earlier and included a negative zero  This patch 
pessimistically assumes that if the equivalence contains zero, we should 
include both + and - 0 in the equivalence that we utilize.

I audited the other places, and found no other place where this issue 
might arise.  Cache propagation is the only place where we augment the 
range with random equivalences.

Bootstrapped on x86_64-pc-linux-gnu with no regressions. Pushed.

Andrew
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Patch

From b0892b1fc637fadf14d7016858983bc5776a1e69 Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacleod@redhat.com>
Date: Mon, 9 Oct 2023 10:15:07 -0400
Subject: [PATCH 2/2] Ensure float equivalences include + and - zero.

A floating point equivalence may not properly reflect both signs of
zero, so be pessimsitic and ensure both signs are included.

	PR tree-optimization/111694
	gcc/
	* gimple-range-cache.cc (ranger_cache::fill_block_cache): Adjust
	equivalence range.
	* value-relation.cc (adjust_equivalence_range): New.
	* value-relation.h (adjust_equivalence_range): New prototype.

	gcc/testsuite/
	* gcc.dg/pr111694.c: New.
---
 gcc/gimple-range-cache.cc       |  3 +++
 gcc/testsuite/gcc.dg/pr111694.c | 19 +++++++++++++++++++
 gcc/value-relation.cc           | 19 +++++++++++++++++++
 gcc/value-relation.h            |  3 +++
 4 files changed, 44 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr111694.c

diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
index 3c819933c4e..89c0845457d 100644
--- a/gcc/gimple-range-cache.cc
+++ b/gcc/gimple-range-cache.cc
@@ -1470,6 +1470,9 @@  ranger_cache::fill_block_cache (tree name, basic_block bb, basic_block def_bb)
 		{
 		  if (rel != VREL_EQ)
 		    range_cast (equiv_range, type);
+		  else
+		    adjust_equivalence_range (equiv_range);
+
 		  if (block_result.intersect (equiv_range))
 		    {
 		      if (DEBUG_RANGE_CACHE)
diff --git a/gcc/testsuite/gcc.dg/pr111694.c b/gcc/testsuite/gcc.dg/pr111694.c
new file mode 100644
index 00000000000..a70b03069dc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr111694.c
@@ -0,0 +1,19 @@ 
+/* PR tree-optimization/111009 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#define signbit(x) __builtin_signbit(x)
+
+static void test(double l, double r)
+{
+  if (l == r && (signbit(l) || signbit(r)))
+    ;
+  else
+    __builtin_abort();
+}
+
+int main()
+{
+  test(0.0, -0.0);
+}
+
diff --git a/gcc/value-relation.cc b/gcc/value-relation.cc
index a2ae39692a6..0326fe7cde6 100644
--- a/gcc/value-relation.cc
+++ b/gcc/value-relation.cc
@@ -183,6 +183,25 @@  relation_transitive (relation_kind r1, relation_kind r2)
   return relation_kind (rr_transitive_table[r1][r2]);
 }
 
+// When one name is an equivalence of another, ensure the equivalence
+// range is correct.  Specifically for floating point, a +0 is also
+// equivalent to a -0 which may not be reflected.  See PR 111694.
+
+void
+adjust_equivalence_range (vrange &range)
+{
+  if (range.undefined_p () || !is_a<frange> (range))
+    return;
+
+  frange fr = as_a<frange> (range);
+  // If range includes 0 make sure both signs of zero are included.
+  if (fr.contains_p (dconst0) || fr.contains_p (dconstm0))
+    {
+      frange zeros (range.type (), dconstm0, dconst0);
+      range.union_ (zeros);
+    }
+ }
+
 // This vector maps a relation to the equivalent tree code.
 
 static const tree_code relation_to_code [VREL_LAST] = {
diff --git a/gcc/value-relation.h b/gcc/value-relation.h
index be6e277421b..31d48908678 100644
--- a/gcc/value-relation.h
+++ b/gcc/value-relation.h
@@ -91,6 +91,9 @@  inline bool relation_equiv_p (relation_kind r)
 
 void print_relation (FILE *f, relation_kind rel);
 
+// Adjust range as an equivalence.
+void adjust_equivalence_range (vrange &range);
+
 class relation_oracle
 {
 public:
-- 
2.41.0