[gcc r11-5021] libstdc++: Remove redundant overflow check for futex timeout [PR 93456]

[gcc r11-5021] libstdc++: Remove redundant overflow check for futex timeout [PR 93456]

[Jonathan Wakely]

https://gcc.gnu.org/g:b8d36dcc917e8a06d8c20b9f5ecc920ed2b9e947

commit r11-5021-gb8d36dcc917e8a06d8c20b9f5ecc920ed2b9e947
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 13 20:57:15 2020 +0000

    libstdc++: Remove redundant overflow check for futex timeout [PR 93456]
    
    The relative_timespec function already checks for the case where the
    specified timeout is in the past, so the difference can never be
    negative. That means we dn't need to check if it's more negative than
    the minimum time_t value.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/93456
            * src/c++11/futex.cc (relative_timespec): Remove redundant check
            negative values.
            * testsuite/30_threads/future/members/wait_until_overflow.cc: Moved to...
            * testsuite/30_threads/future/members/93456.cc: ...here.

Diff:
---
 libstdc++-v3/src/c++11/futex.cc                    | 26 ++++++++++++----------
 .../members/{wait_until_overflow.cc => 93456.cc}   |  0
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/src/c++11/futex.cc b/libstdc++-v3/src/c++11/futex.cc
index 15959cebee5..c008798318c 100644
--- a/libstdc++-v3/src/c++11/futex.cc
+++ b/libstdc++-v3/src/c++11/futex.cc
@@ -73,21 +73,23 @@ namespace
 	return rt;
       }
 
-    auto rel_s = abs_s.count() - now_s;
+    const auto rel_s = abs_s.count() - now_s;
 
-    // Avoid overflows
+    // Convert the absolute timeout to a relative timeout, without overflow.
     if (rel_s > __int_traits<time_t>::__max) [[unlikely]]
-      rel_s = __int_traits<time_t>::__max;
-    else if (rel_s < __int_traits<time_t>::__min) [[unlikely]]
-      rel_s = __int_traits<time_t>::__min;
-
-    // Convert the absolute timeout value to a relative timeout
-    rt.tv_sec = rel_s;
-    rt.tv_nsec = abs_ns.count() - now_ns;
-    if (rt.tv_nsec < 0)
       {
-	rt.tv_nsec += 1000000000;
-	--rt.tv_sec;
+	rt.tv_sec = __int_traits<time_t>::__max;
+	rt.tv_nsec = 999999999;
+      }
+    else
+      {
+	rt.tv_sec = rel_s;
+	rt.tv_nsec = abs_ns.count() - now_ns;
+	if (rt.tv_nsec < 0)
+	  {
+	    rt.tv_nsec += 1000000000;
+	    --rt.tv_sec;
+	  }
       }
 
     return rt;
diff --git a/libstdc++-v3/testsuite/30_threads/future/members/wait_until_overflow.cc b/libstdc++-v3/testsuite/30_threads/future/members/93456.cc
similarity index 100%
rename from libstdc++-v3/testsuite/30_threads/future/members/wait_until_overflow.cc
rename to libstdc++-v3/testsuite/30_threads/future/members/93456.cc