From: Alexandre Oliva <oliva@adacore.com>
Date: Thu, 18 Apr 2024 11:00:59 +0000 (-0300)
Subject: [libstdc++] [testsuite] disable SRA for compare_exchange_padding
X-Git-Tag: basepoints/gcc-15~122
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dcf0bd14cda706be8d0c18963812beefca51df39;p=thirdparty%2Fgcc.git

[libstdc++] [testsuite] disable SRA for compare_exchange_padding

On arm-vx7r2, the uses of as.load() as initializer get SRAed, so the
padding bits in the tests are not what we might expect from full-word
struct copies.

I tried adding a function to perform bitwise copying, but even taking
the as.load() argument by const&, we'd still construct a temporary
with SRAed field-wise copying.  Unable to find another way to ensure
we wouldn't get a temporary, I went for disabling SRA.


for  libstdc++-v3/ChangeLog

	* testsuite/29_atomics/atomic/compare_exchange_padding.cc:
	Disable SRA.
---

diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
index 2f18d426e7f7..a6081968ca86 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
@@ -1,6 +1,7 @@
 // { dg-do run { target c++20 } }
 // { dg-require-atomic-cmpxchg-word "" }
 // { dg-add-options libatomic }
+// { dg-additional-options "-fno-tree-sra" }
 
 #include <atomic>
 #include <cstring>
@@ -26,10 +27,10 @@ main ()
   s.s = 42;
 
   std::atomic<S> as{ s };
-  auto ts = as.load();
+  auto ts = as.load(); // SRA might prevent copying of padding bits here.
   VERIFY( !compare_struct(s, ts) ); // padding cleared on construction
   as.exchange(s);
-  auto es = as.load();
+  auto es = as.load(); // SRA might prevent copying of padding bits here.
   VERIFY( compare_struct(ts, es) ); // padding cleared on exchange
 
   S n;