Re: Concertlina II: Full Circle

Thomas Koenig wrote:

Terje Mathisen <terje.mathisen@tmsw.no> schrieb:

MitchAlsup1 wrote:

John Savard wrote:
 

On Tue, 18 Jun 2024 21:23:57 +0000, mitchalsup@aol.com (MitchAlsup1)
wrote:

John Savard wrote:

 

(1 bit) This indicates whether we're talking about the integer
registers or the floating-point ones.

>
Loops controlled by floating point indexes do not vectorize, however
the body of the loop can be any mix of int, logical, memory, or FP
instructions.

 

Oh no, my index is always an integer. This bit applies to the
"live-in" bits - if the loop performs floating-point computation, it's
floating-point registers that I want to mark as forwarding nodes.

 See, I do not have this distinction, there is but one file.
 

And so you indicate this explicitly in VVM as well. I tended to assume
only a limited number of registers would be needed to live in, plus I
have both floating and integer register files, hence the differences.

 It ends up that the majority of register uses in a loop do not need to
be visible outside of the loop. This is almost the contrapositive of
annotating which registers are temporary in the loop. 90%+ of loops do not even need the index register to be live outside of the loop.

>
This is partly due to programming languages that applies lifetimes to variables, so that an index register which is defined in the
scaffolding
 of the loop (i.e. for (i = 0; i < limit; i++) {}) is invisible as soon as the loop terminates.

This makes things more clear to anybody reading the code (and
unambiguous to the compiler).  However, lifetime analysis has
also become very good, and if the value is not used afterwards,
I expect no difference in practice.

When one writes::
     for( uint64_t i = 0; i < max; i++ )
the lifetime of i is explicit--it terminates with the loop.

Without such a restriction, there are many times when it would be very natural to inspect the index in order to determine if this was a normal
 (counting) exit, or an early exit due to some internal test.

Hmm... do you mean for the programmer, or for the compiler?