This patch merges a consecutive sequence of
s_or_saveexec s_o, s_i
s_xor exec, exec, s_o
into a single
s_andn2_saveexec s_o, s_i instruction.
This patch also cleans up the SIOptimizeExecMasking pass a bit.
Reviewed By: nhaehnle
Differential Revision: https://reviews.llvm.org/D129073
The generic legalizer framework is still used to reduce the problem
to scalar multiplication with the bit size a multiple of 32.
Generating optimal code sequences for big integer multiplication is
somewhat tricky and has a number of target-specific intricacies:
- The target has V_MAD_U64_U32 instructions that multiply two 32-bit
factors and add a 64-bit accumulator. Most partial products should
use this instruction.
- The accumulator is mapped to consecutive 32-bit GPRs, and partial-
product multiply-adds can feed the accumulator into each other
directly. (The register allocator's support for that is somewhat
limited, but that only matters for 128-bit integers and larger.)
- OTOH, on some hardware, V_MAD_U64_U32 requires the accumulator
to be stored in an even-aligned pair of GPRs. To avoid excessive
register copies, it makes sense to compute odd partial products
separately from even partial products (where a partial product
src0[j0] * src1[j1] is "odd" if j0 + j1 is odd) and add both
halves together as a final step.
- We can combine G_MUL+G_ADD into a single cascade of multiply-adds.
- The target can keep many carry-bits in flight simultaneously, so
combining carries using G_UADDE is preferable over G_ZEXT + G_ADD.
- Not addressed by this patch: When the factors are sign-extended,
the V_MAD_I64_I32 instruction (signed version!) can be used.
It is difficult to address these points generically:
1) Finding matching pairs of G_MUL and G_UMULH to find a wide
multiply is expensive. We could add a G_UMUL_LOHI generic instruction
and conditionally use that in the generic legalizer, but by itself
this wouldn't allow us to use the accumulation capability of
V_MAD_U64_U32. One could attempt to find matching G_ADD + G_UADDE
post-legalization, but this is also expensive.
2) Similarly, making sense of the legalization outcome of a wide
pre-legalization G_MUL+G_ADD pair is extremely expensive.
3) How could the generic legalizer possibly deal with the
particular idiosyncracy of "odd" vs. "even" partial products.
All this points in the direction of directly emitting an ideal code
sequence during legalization, but the generic legalizer should not
be burdened with such overly target-specific concerns. Hence, a
custom legalization.
Note that the implemented approach is different from that used by
SelectionDAG because narrowing of scalars works differently in
general. SelectionDAG iteratively cuts wide scalars into low and
high halves until a legal size is reached. By contrast, GlobalISel
does the narrowing in a single shot, which should be better for
compile-time and for the quality of the generated code.
This patch leaves three gaps open:
1. When the factors are uniform, we should execute the multiplication on
the SALU. Register bank mapping already ensures this.
However, the resulting code sequence is not optimal because it doesn't
fully use the carry-in capabilities of S_ADDC_U32. (V_MAD_U64_U32
doesn't have a carry-in.) It is very difficult to fix this after the
fact, so we should really use a different legalization sequence in
this case. Unfortunately, we don't have a divergence analysis and so
cannot make that choice.
(This only matters for 128-bit integers and larger.)
2. Avoid unnecessary multiplies when sources are known to be zero- or
sign-extended. The challenge is that the legalizer does not currently
have access to GISelKnownBits.
3. When the G_MUL is followed by a G_ADD, we should consider combining
the two instructions into a single multiply-add sequence, to utilize
the accumulator of V_MAD_U64_U32 fully. (Unless the multiply has
multiple uses and the implied duplication of the multiply is an
overall negative). However, this is also not true when the factors
are uniform: in that case, it is generally better to *not* combine
the two operations, so that the multiply can be done on the SALU.
Again, we don't have a divergence analysis available and so cannot
make an informed choice.
Differential Revision: https://reviews.llvm.org/D124844
Fold immediates regardless of how many uses they have. This is expected
to increase overall code size, but decrease register usage.
Differential Revision: https://reviews.llvm.org/D114644
Previously SIFoldOperands::foldInstOperand would only fold a
non-inlinable immediate into a single user, so as not to increase code
size by adding the same 32-bit literal operand to many instructions.
This patch removes that restriction, so that a non-inlinable immediate
will be folded into any number of users. The rationale is:
- It reduces the number of registers used for holding constant values,
which might increase occupancy. (On the other hand, many of these
registers are SGPRs which no longer affect occupancy on GFX10+.)
- It reduces ALU stalls between the instruction that loads a constant
into a register, and the instruction that uses it.
- The above benefits are expected to outweigh any increase in code size.
Differential Revision: https://reviews.llvm.org/D114643
In some cases StructurizeCFG inserts i1 xor instructions to invert
predicates. Add a quick loop to clean these up afterwards if we can get
away with modifying an existing compare instruction instead.
(StructurizeCFG is generally run late in the pipeline so instcombine
does not clean them up for us.)
Differential Revision: https://reviews.llvm.org/D118623
This reverts commit a6b54ddaba2d5dc0f72dcc4591c92b9544eb0016.
Apparently it is not safe to modify the condition even if it passes the
hasOneUse test, because StructurizeCFG might have other references to
the condition that are not manifest in the IR use-def chains.
This avoids various cases where StructurizeCFG would otherwise insert an
xor i1 instruction, and it since it generally runs late in the pipeline,
instcombine does not clean up the xor-of-cmp pattern.
Differential Revision: https://reviews.llvm.org/D118478
For AMDGPU, any use of the physical register EXEC prevents sinking even if it is not a real physical register read. Add check to see if a physical
register use can be ignored for sinking.
Also perform same constant and ignorable physical register check when considering sinking in loops.
https://reviews.llvm.org/D116053
Artifact combiner is not able to access individual elements after using
LCMTy style merge/unmerge, extract and insert to change vector number of
elements (pad with undef or split to sub-vector instructions).
Use unmerge to individual elements instead and then merge elements into
requested types.
Change argument lowering for vectors and moreElementsVector to use
buildPadVectorWithUndefElements and buildDeleteTrailingVectorElements.
FewerElementsVector had a few helpers that had different behavior,
introduce new helper for most of the opcodes.
FewerElementsVector helper is more flexible since it can create leftover
instruction smaller then requested type (useful in case target wants to
avoid pad with undef and use fewer registers). If target does not want
leftover of different type it should call more elements first.
Some helpers were performing more elements first to have split without
leftover. Opcodes that used this helper use clampMaxNumElementsStrict
(does more elements first) in LegalizerInfo to avoid test changes.
Fixes failures caused by failing to combine artifacts created during
more/fewer elements vector.
Differential Revision: https://reviews.llvm.org/D114198
The compiler was generating symbols in the final code object for local
branch target labels. This bloats the code object, slows down the loader,
and is only used to simplify disassembly.
Use '--symbolize-operands' with llvm-objdump to improve readability of the
branch target operands in disassembly.
Fixes: SWDEV-312223
Reviewed By: scott.linder
Differential Revision: https://reviews.llvm.org/D114273
The old expansion open-coded a 64-bit addition in a strange way, by
adding the high parts *without* carry-in from the low part, and then
adding the carry back in later on. Fixing this saves a couple of
instructions and makes the code much easier to understand.
Differential Revision: https://reviews.llvm.org/D113679
This simple heuristic uses the estimated live range length combined
with the number of registers in the class to switch which heuristic to
use. This was taking the raw number of registers in the class, even
though not all of them may be available. AMDGPU heavily relies on
dynamically reserved numbers of registers based on user attributes to
satisfy occupancy constraints, so the raw number is highly misleading.
There are still a few problems here. In the original testcase that
made me notice this, the live range size is incorrect after the
scheduler rearranges instructions, since the instructions don't have
the original InstrDist offsets. Additionally, I think it would be more
appropriate to use the number of disjointly allocatable registers in
the class. For the AMDGPU register tuples, there are a large number of
registers in each tuple class, but only a small fraction can actually
be allocated at the same time since they all overlap with each
other. It seems we do not have a query that corresponds to the number
of independently allocatable registers. Relatedly, I'm still debugging
some allocation failures where overlapping tuples seem to not be
handled correctly.
The test changes are mostly noise. There are a handful of x86 tests
that look like regressions with an additional spill, and a handful
that now avoid a spill. The worst looking regression is likely
test/Thumb2/mve-vld4.ll which introduces a few additional
spills. test/CodeGen/AMDGPU/soft-clause-exceeds-register-budget.ll
shows a massive improvement by completely eliminating a large number
of spills inside a loop.
Use GCNHazardRecognizer in postra sched.
Updated tests for the new schedules.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D109536
Change-Id: Ia86ba2ae168f12fb34b4d8efdab491f84d936cde
The requested register class priorities weren't respected
globally. Not sure why this is a target option, and not just the
expected behavior (recently added in
1a6dc92be7d68611077f0fb0b723b361817c950c). This avoids an allocation
failure when many wide tuple spills are introduced. I think this is a
workaround since I would not expect the allocation priority to be
required, and only a performance hint. The allocator should be smarter
about when only a subregister needs to be spilled and restored.
This does regress a couple of degenerate store stress lit tests which
shouldn't be too important.
The killed flag is not always set. E.g. when a variable is used in a
loop, it is never marked as killed, although it is unused in following
basic blocks. Also, we try to deprecate kill flags and not use them.
Check if the register is live in the endif block. If not, consider it
killed in the then and else blocks.
The vgpr-liverange tests have two new tests with loops
(pre-committed, so the diff is visible).
I also needed to change the subtarget to gfx10.1, otherwise calls
are not working.
Differential Revision: https://reviews.llvm.org/D106291
This is to allow 64 bit constant rematerialization. If a constant
is split into two separate moves initializing sub0 and sub1 like
now RA cannot rematerizalize a 64 bit register.
This gives 10-20% uplift in a set of huge apps heavily using double
precession math.
Fixes: SWDEV-292645
Differential Revision: https://reviews.llvm.org/D104874
This pass aims to optimize VGPR live-range in a typical divergent if-else
control flow. For example:
def(a)
if(cond)
use(a)
... // A
else
use(a)
As AMDGPU access vgpr with respect to active-mask, we can mark `a` as
dead in region A. For details, please refer to the comments in
implementation file.
The pass is enabled by default, the frontend can disable it through
"-amdgpu-opt-vgpr-liverange=false".
Differential Revision: https://reviews.llvm.org/D102212
Use existing KnownBits helpers from KnownBits.h to simplify G_ICMPs.
E.g.
x == x -> true
x != x -> false
load(x) > 1 -> true (when the load is known to be greater than 1)
And so on.
Differential Revision: https://reviews.llvm.org/D102542
Add a combiner helper that replaces G_UNMERGE of big constants into direct
use of smaller constants.
Differential Revision: https://reviews.llvm.org/D87166
This combine previously tried to take sequences like:
%cond = G_ICMP pred, a, b
G_BRCOND %cond, %truebb
G_BR %falsebb
%truebb:
...
%falsebb:
...
and by inverting the compare predicate and swapping branch targets, delete the
G_BR and instead have a single conditional branch to the falsebb. Since in an
earlier patch we have a combine to fold not(icmp) into just an inverted icmp,
we don't need this combine to do as much. This patch instead generalizes the
combine by just looking for:
G_BRCOND %cond, %truebb
G_BR %falsebb
%truebb:
...
%falsebb:
...
and then inverting the condition using a not (xor). The xor can be folded away
in a separate combine. This change also lets us avoid some optimization code
in the IRTranslator.
I also think that deleting G_BRs in the combiner is unnecessary. That's
something that targets can decide to do at selection time and could simplify
generic code in future.
Differential Revision: https://reviews.llvm.org/D86664
This is needed for an upcoming change to how we translate conditional branches
which might generate these.
Differential Revision: https://reviews.llvm.org/D86383
By detecting this sign extend pattern early, we can uncover opportunities for
more optimizations.
Differential Revision: https://reviews.llvm.org/D85965
