(kudu) branch master updated: [g++11] Fix DecrementIntCell for g++10 and g++11

[alexey]

This is an automated email from the ASF dual-hosted git repository.

alexey pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/kudu.git


The following commit(s) were added to refs/heads/master by this push:
     new 1f0c0b017 [g++11] Fix DecrementIntCell for g++10 and g++11
1f0c0b017 is described below

commit 1f0c0b0172fb211e74848c87fce983e45280e66d
Author: Zoltan Martonka <zmarto...@gmail.com>
AuthorDate: Fri May 3 12:02:44 2024 +0000

    [g++11] Fix DecrementIntCell for g++10 and g++11
    
    There seems to be a compiler bug, that optimizes out the safety check
    for INT_MIN in the DecrementIntCell function. It appears on RHEL 9.2
    with g++ 11.4.1. Only in Release build. For more infoi, see:
    
    
https://stackoverflow.com/questions/78424303/g-optimizes-away-check-for-int-min-in-release-build
    
    The issue seems to be fixed in g++12 and not yet present in g++9.
    
    Solution:
    Slightly change the function to ensure it is compiled correctly.
    This modification should not alter the correct optimized code.
    
    Basically, any change where the compiler cannot perform the two
    optimization steps (in this order) should address the issue:
    
    + if (x == INT_MIN) x = INT_MAX; else x -= 1; ====> x -= 1
    (this is equivalent on the x86 platform).
    + if (x - 1 < x) ====> if (true)
    (this equivalence holds only at the mathematical level).
    
    Change-Id: Ia3cea2849a88c4d7e2587ceb805cd3258652e3c5
    Reviewed-on: http://gerrit.cloudera.org:8080/21396
    Tested-by: Alexey Serbin <ale...@apache.org>
    Reviewed-by: Alexey Serbin <ale...@apache.org>
---
 src/kudu/common/key_util.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/kudu/common/key_util.cc b/src/kudu/common/key_util.cc
index 290c4b28e..280804f48 100644
--- a/src/kudu/common/key_util.cc
+++ b/src/kudu/common/key_util.cc
@@ -118,7 +118,7 @@ bool DecrementIntCell(void* cell_ptr) {
     // Signed overflow is undefined in C. So, we'll use a branch here
     // instead of counting on undefined behavior.
     if (orig == MathLimits<cpp_type>::kMin) {
-      dec = MathLimits<cpp_type>::kMax;
+      return false;
     } else {
       dec = orig - 1;
     }