nothrow by default
gregormueckl at gmx.de
Fri Jan 10 14:52:45 UTC 2020
On Friday, 10 January 2020 at 07:06:31 UTC, Walter Bright wrote:
> On 1/9/2020 7:42 PM, Gregor Mückl wrote:
>> What exactly is the execution overhead for non-throwing code
>> I believe I understand the overhead once stack unwinding needs
>> to be performed, but how is code generation affected for the
>> normal path?
> You need a mechanism for jumping to the scope guard code. Can't
> do any code motion optimizations across the boundaries of such
> code. Can't do register assignments for variables that are
> "live" across that boundary.
> Just write some code with destructors in C++, compile it with
> and without exceptions enabled, and dump the generated
I played around with this as you suggested. The most concise
example that I could find where -fno-exceptions makes a
difference is this:
The version with exceptions reserves a register for something at
the start of the function (rbp in this case), but I can't tell
what it's for. It is used in the unwinding handler that is
appended to the function after the ret instruction.
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