This enables subreg liveness in the arm backend when MVE is present,
which allows the register allocator to detect when subregister are
alive/dead, compared to only acting on full registers. This can helps
produce better code on MVE with the way MQPR registers are made up of
SPR registers, but is especially helpful for MQQPR and MQQQQPR
registers, where there are very few "registers" available and being able
to split them up into subregs can help produce much better code.
Differential Revision: https://reviews.llvm.org/D107642
This strips out a lot of the code that should no longer be needed from
the MVETailPredictionPass, leaving the important part - find active lane
mask instructions and convert them to VCTP operations.
Differential Revision: https://reviews.llvm.org/D91866
This hints the operand of a t2DoLoopStart towards using LR, which can
help make it more likely to become t2DLS lr, lr. This makes it easier to
move if needed (as the input is the same as the output), or potentially
remove entirely.
The hint is added after others (from COPY's etc) which still take
precedence. It needed to find a place to add the hint, which currently
uses the post isel custom inserter.
Differential Revision: https://reviews.llvm.org/D89883
This changes the definition of t2DoLoopStart from
t2DoLoopStart rGPR
to
GPRlr = t2DoLoopStart rGPR
This will hopefully mean that low overhead loops are more tied together,
and we can more reliably generate loops without reverting or being at
the whims of the register allocator.
This is a fairly simple change in itself, but leads to a number of other
required alterations.
- The hardware loop pass, if UsePhi is set, now generates loops of the
form:
%start = llvm.start.loop.iterations(%N)
loop:
%p = phi [%start], [%dec]
%dec = llvm.loop.decrement.reg(%p, 1)
%c = icmp ne %dec, 0
br %c, loop, exit
- For this a new llvm.start.loop.iterations intrinsic was added, identical
to llvm.set.loop.iterations but produces a value as seen above, gluing
the loop together more through def-use chains.
- This new instrinsic conceptually produces the same output as input,
which is taught to SCEV so that the checks in MVETailPredication are not
affected.
- Some minor changes are needed to the ARMLowOverheadLoop pass, but it has
been left mostly as before. We should now more reliably be able to tell
that the t2DoLoopStart is correct without having to prove it, but
t2WhileLoopStart and tail-predicated loops will remain the same.
- And all the tests have been updated. There are a lot of them!
This patch on it's own might cause more trouble that it helps, with more
tail-predicated loops being reverted, but some additional patches can
hopefully improve upon that to get to something that is better overall.
Differential Revision: https://reviews.llvm.org/D89881
Fix the ARM backend's analyzeBranch so it doesn't ignore predicated
return instructions, and make the MachineVerifier rule more strict.
Differential Revision: https://reviews.llvm.org/D40061
This adapts legalization of intrinsic get.active.lane.mask to the new semantics
as described in D86147. Because the second argument is now the loop tripcount,
we legalize this intrinsic to an 'icmp ULT' instead of an ULE when it was the
backedge-taken count.
Differential Revision: https://reviews.llvm.org/D86302
This adapts tail-predication to the new semantics of get.active.lane.mask as
defined in D86147. This means that:
- we can remove the BTC + 1 overflow checks because now the loop tripcount is
passed in to the intrinsic,
- we can immediately use that value to setup a counter for the number of
elements processed by the loop and don't need to materialize BTC + 1.
Differential Revision: https://reviews.llvm.org/D86303
This refactors option -disable-mve-tail-predication to take different arguments
so that we have 1 option to control tail-predication rather than several
different ones.
This is also a prep step for D82953, in which we want to reject reductions
unless that is requested with this option.
Differential Revision: https://reviews.llvm.org/D83133
This patch stops the trunc, rint, round, floor and ceil intrinsics from blocking tail predication.
Differential Revision: https://reviews.llvm.org/D82553
David Green