On 13/10/2019 01:54, Ben Grasset wrote:
I guess this doesn't matter too much in the grand scheme of things,
but I'm somewhat confused by it, so I thought I'd ask.
Specifically, the reporter of that issue, calling themselves
"Alexander", used the following program as an "example" of what they
called "too aggressive optimization":
program test:
var v:longword;
begin
if v=2 then while true do ;
end.
To me, that just shows a while loop that will very obviously be exited
immediately in all cases, because "v" is very obviously *not* equal to
2. Yet they used a (tiny) snippet of assembler from this and deemed it
"incorrect", without making any attempt to clarify what they meant.
The fix does not appear to be about the "if v=2" part.
But about the "while constant_expression_with_no_sideeffects do
{nothing};" empty loop.
Also in the bug report the "cmpl $2" was not removed.
So the compiler detect the dead code. (caused by v <> 2 / which probably
is not the case in the users real code).
The compile does remove an empty loop.
An empty loop, with a condition that also does nothing, that is a loop
that does nothing. Except it does: It loops forever, and stops the code
after it from being executed.
---
I guess it is just an overlap, that the "if v=2" (which may be needed to
trigger the issue in a minimal example) could/should/might trigger
another optimization (which however is not actually triggered).
That at least is what I would figure from the data avail
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