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Re: [Qemu-devel] [PATCH 01/11] tci: Fix build regression

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 01/11] tci: Fix build regression
Date: Thu, 7 Apr 2016 20:40:26 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1

On 04/07/2016 01:37 PM, Stefan Weil wrote:
I just tested a variant with tcg_debug_assert. It creates less efficient
code when debugging is disabled. Here is the code size for x86_64:

with normal tcg_debug_assert:

    text       data        bss        dec        hex    filename
    8293          0        128       8421       20e5

In gdb I can also see assembler code for op_size at the beginning
of the for loop in tcg_qemu_tb_exec. This slows down the interpreter.

Please file a gcc bug.

A branch across __builtin_unreachable is supposed to fold to a simple compile-time assert, providing extra information to the compiler but not generating code.


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