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The phi classes are no longer in a union-find
structure, instead each temporary argument of
a phi node gets a pointer to it. The hinting
of the phi node is then shared with its the
one of its arguments. When liveness proceeds
and finds out that two elements with same
hinting (a phi node and one of its arguments
or two arguments of the same phi node)
interfere, one of them has its phi pointer
reset, that way, the hinting won't be shared.
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At the beginning of each block look at the phi nodes that
have some arguments already allocated. If the some
arguments from blocks with high execution frequency are
all assigned 'r', reset the the hint for the phi node to
this 'r'. Combined with the following heuristic, this
can save some copies at the end of the destination blocks.
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I thought that many parallel copies generated
can be avoided if temporaries are in their hint
register at the beginning of blocks with multiple
predecessors.
To get more benefit, I suspect that we could
use a copy-propagating peephole pass.
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valloc is actually a POSIX function that
prevents compilation on some systems.
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The detection of empty permutations was incorrect
since the changes made to the vector routines.
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When rdx is used to return a value and is used as argument,
it is in the call defs and hence made dead by the loop
modified here. This is obviously erroneous behavior.
We instead rephrase the loop to make it clear that among
the caller-save registers, only the ones used by the call
must be live before the call.
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The IR generated by calls was very bulky because two
instructions were used for marking the live range of
a clobber.
This patch attempts to store the information of what
registers are use/def/clobber in the call instruction
itself, this leads to more compact code (even more
when we'll have SSE registers). However, I find that
the amount of extra code needed is not really
easonable. Fortunately it is not too invasive, thus
if the complexity creeps in, it should be easy to
revert.
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revert commit d0e9e3ada106dfe8dcda7a0099b341000f00afb2.
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I could never figure out a correct version
without the tests. I'm now fairly confident
dopm() will work as we need it to.
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The old code was broken for sure, this one might
be. I have to create a test bench for the dopm
function. It would also test the parallel move
lowering (pmgen and folks).
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The first one was not so bad, when we a parallel move
clobbers one machine register in use, we used to
free the temporary t* using it, mark the register as
unavailable and allocate a new location for the
t*. But this fails when all the registers are in use.
In that case, the destination of the move must be in
a register r1, so I require a swap of the register
to copy (used by t*) with r1 and update the map
accordingly.
I would like to move all the above logic in a function
dealing with clobbers in general.
The second bug is in the parallel move compiler, this
one was a little more nasty and could have caused much
debugging pain. It would be reasonable to test it in
a similar way that I did for the slota() allocator.
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An invariant is that all registers allocated at some point
have a hint. This makes the code removed by this commit
dead because of the if condition testing for empty hints.
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We only allocate a register that has a hint if the
hint register is not used already. In the max example
it gives a better result and it does not seem to affect
the collatz test.
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It could very well be that the temporary we
assign already got assigned to the right
register! Good things happen.
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There was a typo that made always the same successor
to be selected for register allocation hinting.
Also, I now attempt to prioritize hints over succeccor's
choices as it appears to give slightly better results...
Now that I think about it, the code re-using the most
frequent successor block's assignment might be dead
because all registers have hints if they got assigned
once. To investigate.
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This is possible because we know that they are
represented by different integers.
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