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* [gcc/devel/c++-modules] tree-optimization/94103 avoid CSE of loads with padding
@ 2020-03-19 12:41 Nathan Sidwell
0 siblings, 0 replies; only message in thread
From: Nathan Sidwell @ 2020-03-19 12:41 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:1dc00a8ec9aeba86b74b16bff6f171824bb7b4a1
commit 1dc00a8ec9aeba86b74b16bff6f171824bb7b4a1
Author: Richard Biener <rguenther@suse.de>
Date: Thu Mar 12 14:18:35 2020 +0100
tree-optimization/94103 avoid CSE of loads with padding
VN currently replaces a load of a 16 byte entity 128 bits of precision
(TImode) with the result of a load of a 16 byte entity with 80 bits of
mode precision (XFmode). That will go downhill since if the padding
bits are not actually filled with memory contents those bits are
missing.
2020-03-12 Richard Biener <rguenther@suse.de>
PR tree-optimization/94103
* tree-ssa-sccvn.c (visit_reference_op_load): Avoid type
punning when the mode precision is not sufficient.
* gcc.target/i386/pr94103.c: New testcase.
Diff:
---
gcc/ChangeLog | 6 ++++++
gcc/testsuite/ChangeLog | 5 +++++
gcc/testsuite/gcc.target/i386/pr94103.c | 17 +++++++++++++++++
gcc/tree-ssa-sccvn.c | 23 ++++++++++++++++-------
4 files changed, 44 insertions(+), 7 deletions(-)
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 22ba5ed36e6..a43b453178d 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-03-12 Richard Biener <rguenther@suse.de>
+
+ PR tree-optimization/94103
+ * tree-ssa-sccvn.c (visit_reference_op_load): Avoid type
+ punning when the mode precision is not sufficient.
+
2020-03-12 H.J. Lu <hongjiu.lu@intel.com>
PR target/89229
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index a1f0e3a18c5..a5730ebbbc0 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-12 Richard Biener <rguenther@suse.de>
+
+ PR tree-optimization/94103
+ * gcc.target/i386/pr94103.c: New testcase.
+
2020-03-12 Tobias Burnus <tobias@codesourcery.com>
PR middle-end/94120
diff --git a/gcc/testsuite/gcc.target/i386/pr94103.c b/gcc/testsuite/gcc.target/i386/pr94103.c
new file mode 100644
index 00000000000..91b5fc64b5e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr94103.c
@@ -0,0 +1,17 @@
+/* { dg-do run { target lp64 } } */
+/* { dg-options "-O3" } */
+
+int main()
+{
+ long double x;
+ unsigned long u[2] = {0xEEEEEEEEEEEEEEEEUL, 0xEEEEEEEEEEEEEEEEUL};
+ __builtin_memcpy(&x, &u, sizeof x);
+ __builtin_memcpy(&u, &x, sizeof u);
+ ++*(unsigned char *)&x;
+ (void)-x;
+ __builtin_memcpy(&u, &x, sizeof u);
+ if (u[1] != 0xEEEEEEEEEEEEEEEEUL
+ || u[0] != 0xEEEEEEEEEEEEEEEFUL)
+ __builtin_abort ();
+ return 0;
+}
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index b7174cd603f..150ddad3e69 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -4899,13 +4899,22 @@ visit_reference_op_load (tree lhs, tree op, gimple *stmt)
if (result
&& !useless_type_conversion_p (TREE_TYPE (result), TREE_TYPE (op)))
{
- /* We will be setting the value number of lhs to the value number
- of VIEW_CONVERT_EXPR <TREE_TYPE (result)> (result).
- So first simplify and lookup this expression to see if it
- is already available. */
- gimple_match_op res_op (gimple_match_cond::UNCOND,
- VIEW_CONVERT_EXPR, TREE_TYPE (op), result);
- result = vn_nary_build_or_lookup (&res_op);
+ /* Avoid the type punning in case the result mode has padding where
+ the op we lookup has not. */
+ if (maybe_lt (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (result))),
+ GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (op)))))
+ result = NULL_TREE;
+ else
+ {
+ /* We will be setting the value number of lhs to the value number
+ of VIEW_CONVERT_EXPR <TREE_TYPE (result)> (result).
+ So first simplify and lookup this expression to see if it
+ is already available. */
+ gimple_match_op res_op (gimple_match_cond::UNCOND,
+ VIEW_CONVERT_EXPR, TREE_TYPE (op), result);
+ result = vn_nary_build_or_lookup (&res_op);
+ }
+
/* When building the conversion fails avoid inserting the reference
again. */
if (!result)
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