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[3/3,v2] tree-optimization/114659 - VN and FP to int punning

Message ID 20240730101902.977C3385C6C0@sourceware.org
State New
Headers show
Series [1/3,v2] Add TARGET_MODE_CAN_TRANSFER_BITS | expand

Commit Message

Richard Biener July 30, 2024, 10:18 a.m. UTC 
The following addresses another case where x87 FP loads mangle the
bit representation and thus are not suitable for a representative
in other types.  VN was value-numbering a later integer load of 'x'
as the same as a former float load of 'x'.

We can use the new TARGET_MODE_CAN_TRANSFER_BITS hook to identify
problematic modes and enforce strict compatibility for those in
the reference comparison, improving the handling of modes with
padding in visit_reference_op_load.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

	PR tree-optimization/114659
	* tree-ssa-sccvn.cc (visit_reference_op_load): Do not
	prevent punning from modes with padding here, but ...
	(vn_reference_eq): ... ensure this here, also honoring
	types with modes that cannot act as bit container.

	* gcc.target/i386/pr114659.c: New testcase.
---
 gcc/testsuite/gcc.target/i386/pr114659.c | 62 ++++++++++++++++++++++++
 gcc/tree-ssa-sccvn.cc                    | 11 ++---
 2 files changed, 66 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr114659.c
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Patch

diff --git a/gcc/testsuite/gcc.target/i386/pr114659.c b/gcc/testsuite/gcc.target/i386/pr114659.c
new file mode 100644
index 00000000000..e1e24d55687
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr114659.c
@@ -0,0 +1,62 @@ 
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+int
+my_totalorderf (float const *x, float const *y)
+{
+  int xs = __builtin_signbit (*x);
+  int ys = __builtin_signbit (*y);
+  if (!xs != !ys)
+    return xs;
+
+  int xn = __builtin_isnan (*x);
+  int yn = __builtin_isnan (*y);
+  if (!xn != !yn)
+    return !xn == !xs;
+  if (!xn)
+    return *x <= *y;
+
+  unsigned int extended_sign = -!!xs;
+  union { unsigned int i; float f; } xu = {0}, yu = {0};
+  __builtin_memcpy (&xu.f, x, sizeof (float));
+  __builtin_memcpy (&yu.f, y, sizeof (float));
+  return (xu.i ^ extended_sign) <= (yu.i ^ extended_sign);
+}
+
+static float
+positive_NaNf ()
+{
+  float volatile nan = 0.0f / 0.0f;
+  return (__builtin_signbit (nan) ? - nan : nan);
+}
+
+typedef union { float value; unsigned int word[1]; } memory_float;
+
+static memory_float
+construct_memory_SNaNf (float quiet_value)
+{
+  memory_float m;
+  m.value = quiet_value;
+  m.word[0] ^= (unsigned int) 1 << 22;
+  m.word[0] |= (unsigned int) 1;
+  return m;
+}
+
+memory_float x[7] =
+  {
+    { 0 },
+    { 1e-5 },
+    { 1 },
+    { 1e37 },
+    { 1.0f / 0.0f },
+  };
+
+int
+main ()
+{
+  x[5] = construct_memory_SNaNf (positive_NaNf ());
+  x[6] = (memory_float) { positive_NaNf () };
+  if (! my_totalorderf (&x[5].value, &x[6].value))
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index dc377fa16ce..0639ba426ff 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -837,6 +837,9 @@  vn_reference_eq (const_vn_reference_t const vr1, const_vn_reference_t const vr2)
 		    TYPE_VECTOR_SUBPARTS (vr2->type)))
 	return false;
     }
+  else if (TYPE_MODE (vr1->type) != TYPE_MODE (vr2->type)
+	   && !mode_can_transfer_bits (TYPE_MODE (vr1->type)))
+    return false;
 
   i = 0;
   j = 0;
@@ -5814,13 +5817,7 @@  visit_reference_op_load (tree lhs, tree op, gimple *stmt)
   if (result
       && !useless_type_conversion_p (TREE_TYPE (result), TREE_TYPE (op)))
     {
-      /* Avoid the type punning in case the result mode has padding where
-	 the op we lookup has not.  */
-      if (TYPE_MODE (TREE_TYPE (result)) != BLKmode
-	  && maybe_lt (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (result))),
-		       GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (op)))))
-	result = NULL_TREE;
-      else if (CONSTANT_CLASS_P (result))
+      if (CONSTANT_CLASS_P (result))
 	result = const_unop (VIEW_CONVERT_EXPR, TREE_TYPE (op), result);
       else
 	{