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https://issues.apache.org/jira/browse/IMPALA-5031?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16623815#comment-16623815
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ASF subversion and git services commented on IMPALA-5031:
---------------------------------------------------------
Commit b727bb03fda35e4c955277a55e81bf57bfb99690 in impala's branch
refs/heads/master from [~jbapple]
[ https://git-wip-us.apache.org/repos/asf?p=impala.git;h=b727bb0 ]
IMPALA-5031: undefined behavior: codegen signed overflow
This patch changes the way signed integer arithmetic is performed in
generated code. It uses unsigned arithmetic instead, because overflow
causes undefined behavior according to the standard.
Compiling with -full_ubsan, the following types of errors are avoided
by this patch:
exprs/operators-ir.cc:167:803: runtime error: signed integer
overflow: -9223372036854775807 + -9223372036854775807 cannot be
represented in type 'long'
exprs/operators-ir.cc:168:823: runtime error: signed integer
overflow: -9223372036854775807 - 9223372036854775807 cannot be
represented in type 'long'
exprs/operators-ir.cc:169:823: runtime error: signed integer
overflow: -9223372036854775807 * -9223372036854775807 cannot be
represented in type 'long'
This is visible when running be/build/latest/exprs/expr-test
--gtest_filter=ExprTest.ArithmeticExprs
To check for performance regressions, I ran TPCH and TPCDS at scale
factor 20 with three minicluster nodes and observed no performance
changes. I also checked the LLVM IR to see that the generated code
after this commit is identical to the generated code at the previous
commit, except that the new code doesn't use the 'nsw' modifier. That
modifier normally indicates that signed wrap does not occur; in this
case the operation happens on unsigned representation of the same
bits, that modifier is no longer relevant.
Change-Id: I79ec3a5ed974709e5e47be6b074d39ee89461f7f
Reviewed-on: http://gerrit.cloudera.org:8080/11406
Reviewed-by: Jim Apple <[email protected]>
Tested-by: Impala Public Jenkins <[email protected]>
> UBSAN clean and method for testing UBSAN cleanliness
> ----------------------------------------------------
>
> Key: IMPALA-5031
> URL: https://issues.apache.org/jira/browse/IMPALA-5031
> Project: IMPALA
> Issue Type: Task
> Components: Backend, Infrastructure
> Affects Versions: Impala 2.9.0
> Reporter: Jim Apple
> Assignee: Jim Apple
> Priority: Minor
>
> http://releases.llvm.org/3.8.0/tools/clang/docs/UndefinedBehaviorSanitizer.html
> builds are supported after https://gerrit.cloudera.org/#/c/6186/, but
> Impala's test suite triggers many errors under UBSAN. Those errors should be
> fixed and then there should be a way to run the test suite under UBSAN and
> fail if there were any errors detected.
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