[llvm-dev] About CodeGen quality

[陳韋任 via llvm-dev]

I guess it tends not to block cross block optimization opportunity, or it
just happen
https://reviews.llvm.org/D30416 is one?

Regards,
chenwj

2017-06-17 1:49 GMT+08:00 Friedman, Eli via llvm-dev <
llvm-dev at lists.llvm.org>:

> On 6/15/2017 11:13 PM, Ehsan Amiri wrote:
>
>
> Forgot to reply to all
>
> Hi Eli
>
> We want to read S->b for example. The size of struct S is 64 bits, and
> seems LLVM treats it as i64.
> Below is the IR corresponding to S->b, IIRC.
>
>     %0 = load i64, *i64 ptr, align 4;
>     %1 = %0 lshr 8;
>     %2 = %1 and 255;
>
>
> This looks fine.
>
>
> Why can't we expect InstCombine to simplify this to an 8 bit load,
> assuming each of %0 and %1 has only one use ?
>
>
> We don't aggressively narrow loads and stores in IR because it tends to
> block other optimizations.  See https://reviews.llvm.org/D30416.
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>


-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170617/3f1512c7/attachment.html>