Mesa (staging/20.1): meson: Disable GCC's dead store elimination for memory zeroing custom new

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Module: Mesa
Branch: staging/20.1
Commit: 979ae78318c3e37cc0e0579b8d1f05c46bb76e7d
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=979ae78318c3e37cc0e0579b8d1f05c46bb76e7d

Author: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Date:   Tue May 19 20:35:49 2020 +0300

meson: Disable GCC's dead store elimination for memory zeroing custom new

Some classes use custom new operator which zeroes memory, however gcc does
aggressive dead-store elimination which threats all writes to the memory
before the constructor as "dead stores".

For now we disable this optimization.

The new operators in question are declared via:
 DECLARE_RZALLOC_CXX_OPERATORS
 DECLARE_LINEAR_ZALLOC_CXX_OPERATORS

The issue was found with lto builds, however there is no guarantee that
it didn't happen with ordinary ones.

CC: <mesa-stable at lists.freedesktop.org>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2977
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/1358
Signed-off-by: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5104>
(cherry picked from commit 5500a2b7fc558217bbd4c2a966ab6fcadaed8b3b)

---

 .pick_status.json | 2 +-
 meson.build       | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/.pick_status.json b/.pick_status.json
index dfdaffee448..adb48305d39 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -67,7 +67,7 @@
         "description": "meson: Disable GCC's dead store elimination for memory zeroing custom new",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": null
     },
diff --git a/meson.build b/meson.build
index ba4fdb2a59f..434684c8bcc 100644
--- a/meson.build
+++ b/meson.build
@@ -980,6 +980,11 @@ else
     '-fno-math-errno',
     '-fno-trapping-math',
     '-Qunused-arguments',
+    # Some classes use custom new operator which zeroes memory, however
+    # gcc does aggressive dead-store elimination which threats all writes
+    # to the memory before the constructor as "dead stores".
+    # For now we disable this optimization.
+    '-flifetime-dse=1',
   ]
   # MinGW chokes on format specifiers and I can't get it all working
   if not (cc.get_id() == 'gcc' and host_machine.system() == 'windows')