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Subject: Re: [Qemu-devel] [PATCH 0/8] optimize various tcg_gen() functions
 using extract op
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To: qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>, Richard Henderson <rth@twiddle.net>
Cc: famz@redhat.com

Hi,

The patch set Patchew intented to compile is incorrect, but this error 
worried me:

On 05/10/2017 05:20 PM, no-reply@patchew.org wrote:
> This series failed build test on s390x host. Please find the details below.
[...]
>   CC      mips64-softmmu/target/mips/translate.o
> /var/tmp/patchew-tester-tmp-f7svi4g9/src/target/mips/translate.c: In function ‘gen_bshfl’:
> /var/tmp/patchew-tester-tmp-f7svi4g9/src/target/mips/translate.c:4595:43: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
>              tcg_gen_extract_tl(t1, t0, 8, 0x00FF00FF00FF00FFULL);
>                                            ^~~~~~~~~~~~~~~~~~~~~
> /var/tmp/patchew-tester-tmp-f7svi4g9/src/target/mips/translate.c:4606:44: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
>              tcg_gen_extract_tl(t1, t0, 16, 0x0000FFFF0000FFFFULL);
>                                             ^~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> /var/tmp/patchew-tester-tmp-f7svi4g9/src/rules.mak:69: recipe for target 'target/mips/translate.o' failed
> make[1]: *** [target/mips/translate.o] Error 1
> Makefile:327: recipe for target 'subdir-mips64el-softmmu' failed

Now I tried to use this code on mips64el-softmmu target:

tcg_gen_extract_tl(t1, t0, 5, 0x7ffffffffffffff);

And got:

error: large integer implicitly truncated to unsigned type 
[-Werror=overflow]
              tcg_gen_extract_tl(t1, t0, 5, 0x7ffffffffffffff);
                                            ^~~~~~~~~~~~~~~~~

There is no need for a such operation, but it seems legit.

I think tcg-op.h would be clearer cleaning few 'unsigned/unsigned int' 
by a 'tcg_target_long'. Like:

  void tcg_gen_extract_i64(TCGv_i64 ret, TCGv_i64 arg,
-                         unsigned int ofs, unsigned int len);
+                         unsigned int ofs, tcg_target_long len);

What do you think Richard?

Regards,

Phil.