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From: Skybuck Flying on 6 May 2008 12:35
Hello,

Suppose I have code like so:

Condition1 := True or False; // determined here
Condition2 := True or False; // determined here
Condition3 := True or False; // determined here

for Y := 0 to Height-1 do
begin
for X := 0 to Width-1 do
begin

// ... inner loop ...

if Condition1 then
begin
... condition 1 code ...
end;

if Condition2 then
begin
... condition 2 code ...
end;

if Condition3 then
begin
... condition 3 code ...
end;

// ... inner loop ...

end;
end;

The question is:

How many of these "condition branches" can be added to the inner loop
without getting miss-prediction on for example an AMD X2 3800+ ?

The asm looks something like:

// Condition 1
026B08AA 803C2400 cmp byte ptr [esp],$00
026B08AE 0F8496000000 jz $026b094a

// Condition 1 Code

026B08B4 8B481C mov ecx,[eax+$1c]
....
....
....
....

// Condition 2

I have a further question:

In the manual it says the processor assumes fall throughs ?

So does this mean the processor assumes the "condition x code" is always
taken ?

In other words, the processor does not assume a jump occurs ?

Hmm this seems to be contrary to the loop idea.

Loops jump back, I read the jumps are always followed/assumed taken by the
processor ?

I am confused...

Bye,
Skybuck.


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