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Posted to issues-all@impala.apache.org by "Tim Armstrong (Jira)" <ji...@apache.org> on 2020/08/13 21:29:00 UTC
[jira] [Commented] (IMPALA-3345) Investigate issues with
__builtin_*_overflow in LLVM
[ https://issues.apache.org/jira/browse/IMPALA-3345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17177327#comment-17177327 ]
Tim Armstrong commented on IMPALA-3345:
---------------------------------------
I did try this with newer version of gcc and clang in godbolt and the code generated seemed fine for int64_t
> Investigate issues with __builtin_*_overflow in LLVM
> ----------------------------------------------------
>
> Key: IMPALA-3345
> URL: https://issues.apache.org/jira/browse/IMPALA-3345
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 2.6.0
> Reporter: Tim Armstrong
> Priority: Minor
> Labels: codegen
>
> LLVM 3.8 added support for __builtin_add_overflow and __builtin_mul_overflow. We can use them in decimal-value-inline.h but there are various issues:
> * __builtin_mul_overflow for 128-bit ints (16-byte decimals) generates a reference to a runtime function implemented by LLVM's runtime library but not GCC's (we use the GCC runtime for all code).
> * __builtin_add_overflow seems extremely slow: I saw TPC-H query 1 regress by 3-4x compared to the current code.
> This JIRA is to investigate these issues and see if the functions can be beneficial.
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