The InitUndef pass works around a register allocation issue, where undef
operands can be allocated to the same register as early-clobber result
operands. This may lead to ISA constraint violations, where certain
input and output registers are not allowed to overlap.
Originally this pass was implemented for RISCV, and then extended to ARM
in #77770. I've since removed the target-specific parts of the pass in
#106744 and #107885. This PR reduces the pass to use a single
requiresDisjointEarlyClobberAndUndef() target hook and enables it by
default. The hook is disabled for AMDGPU, because overlapping
early-clobber and undef operands are known to be safe for that target,
and we get significant codegen diffs otherwise.
The motivating case is the one in arm64-ldxr-stxr.ll, where we were
previously incorrectly allocating a stxp input and output to the same
register.
Any SGPR read by a VALU can potentially obscure SALU writes to the same
register.
Insert s_wait_alu instructions to mitigate the hazard on affected paths.
Compute a global cache of SGPRs with any VALU reads and use this to
avoid inserting mitigation for SGPRs never accessed by VALUs.
To avoid excessive search when compile time is priority implement
secondary mode where all SALU writes are mitigated.
Co-authored-by: Shilei Tian <shilei.tian@amd.com>
On GFX11.5 shaders having completed exports need to execute/wait at a
lower priority than shaders still executing exports.
Add code to maintain normal priority of 2 for shaders that export and
drop to priority 0 after exports.
Define subtarget features for atomic fmin/fmax support.
The flat/global support is a real messe. We had float/double support at
the beginning in gfx6 and gfx7. gfx8 removed these. gfx10 reintroduced them.
gfx11 removed the f64 versions again.
gfx9 partially reintroduced them, in gfx90a and gfx940 but only for f64.
Implement GCNSubtarget::checkSubtargetFeatures as a canonical place to
check subtarget features for consistency and diagnose any
inconsistencies. To start with, the implementation just checks that
either wavefrontsize32 or wavefrontsize64 is selected.
checkSubtargetFeatures is called at the start of instruction selection.
This is pretty arbitrary. It is just a convenient point at which we have
access to the subtarget that we're going to use for codegenning a
particular function.
On gfx11 shaders run with PRIV=1, which causes `s_trap 2` to be treated
as a nop, which means it isn't a correct lowering for the trap
intrinsic. As a workaround, this commit instead lowers the trap
intrinsic to instructions that simulate the behavior of s_trap 2.
Fixes: SWDEV-438421
DS atomic fadd F32 does respect the denormal mode, so we do not need to
consider the expected FP mode or unsafe-fp-atomics attribute. They don't
respect the rounding mode, but we don't care outside of strictfp. This
also reveals the fp-mode-is-flush check has been missing in the cases
that should be considering it alongside amdgpu-unsafe-fp-atomics.
This also stops considering the case where flushing is enabled for f64,
as flushing isn't mandated and we barely handle this case.
By default the scheduling info of instructions into a BUNDLE are given a
latency of 0 as they operate on the implicit register of the bundle.
This modifies that for AArch64 so that the latency is adjusted to use
the latency from the instruction in the bundle instead. This essentially
assumes that the bundled instructions are executed in a single cycle,
which for AArch64 is probably OK considering they are mostly used for
MOVPFX bundles, where this can help create slightly better scheduling
especially for in-order cores.
This patch introduces a new command-line option for clang, namely,
amdgpu-precise-mem-op (or precise-memory in the backend). When this option is specified, a waitcnt
instruction is generated after each memory load/store instruction. The
counter values are always 0, but which counters are involved depends on
the memory instruction.
---------
Co-authored-by: Jun Wang <jun.wang7@amd.com>
MIParser checks that implicit operands match the instruction definition,
so they have to be $vcc even in wave32 mode. Use the mirFileLoaded hook
to fix them after MIParser's checks, converting them to $vcc_lo which is
what that rest of CodeGen expects.
This is all just extending the fixImplicitOperands hack which was
introduced with GFX10, but at least it makes it possible to write a MIR
test which creates the same instructions that normal CodeGen would
generate.
gfx11 chips may, in some conditions, behave incorrectly with S_CLAUSE
instructions (hard clauses) containing more than 32 operations (that is,
whose arguments exceed 0x1f). However, gfx10 targets will work
successfully with clauses of up to length 63.
Therefore, define the MaxHardClauseLength property on GCNSubtarget and
make it a subtarget feature via tablegen, thus allowing us to specify,
both now and in the future, the maximum viable size of clauses on
various hardware from the tablegen definition. If MaxHardClauseLength is
0, which is the default, the hardware does not support hard clauses.
These generic targets include multiple GPUs and will, in the future,
provide a way to build once and run on multiple GPU, at the cost of less
optimization opportunities.
Note that this is just doing the compiler side of things, device libs an
runtimes/loader/etc. don't know about these targets yet, so none of them
actually work in practice right now. This is just the initial commit to
make LLVM aware of them.
This contains the documentation changes for both this change and #76954
as well.
Update SIMemoryLegalizer and SIInsertWaitcnts to use separate wait
instructions per counter (e.g. S_WAIT_LOADCNT) and split VMCNT into
separate LOADCNT, SAMPLECNT and BVHCNT counters.
https://github.com/llvm/llvm-project/pull/70634 has disabled use
of potentially negative scratch offsets, but we can use it on GFX12.
---------
Co-authored-by: Stanislav Mekhanoshin <Stanislav.Mekhanoshin@amd.com>
For image and buffer stores the default behaviour on GFX12 is to set all
unset components to the value of the first component. So if we pass only
X component, it will be the same as XXXX, or XY same as XYXX.
This patch simplifies the passed vector of components in InstCombine by
removing components from the end that are equal to the first component.
For image stores it also trims DMask if necessary.
---------
Co-authored-by: Mateja Marjanovic <mmarjano@amd.com>
Modify GCNHazardRecognizer::fixLdsDirectVMEMHazard() so the waitvsrc
operand
in gfx12 DS_PARAM_LOAD or DS_DIRECT_LOAD instructions is set
appropriately
depending on whether a hazard is found or not, rather than inserting an
S_WAITCNT_DEPCTR instruction if a hazard needs to be mitigated.
Co-authored-by: Stephen Thomas <Stephen.Thomas@amd.com>
Consistently treat packed 16-bit operands as 32-bit values, because
that's really what they are. The attempt to treat them differently was
ultimately incorrect and lead to miscompiles, e.g. when using non-splat
constants such as (1, 0) as operands.
Recognize 32-bit float constants for i/u16 instructions. This is a bit
odd conceptually, but it matches HW behavior and SP3.
Remove isFoldableLiteralV216; there was too much magic in the dependency
between it and its use in SIFoldOperands. Instead, we now simply rely on
checking whether a constant is an inline constant, and trying a bunch of
permutations of the low and high halves. This is more obviously correct
and leads to some new cases where inline constants are used as shown by
tests.
Move the logic for switching packed add vs. sub into SIFoldOperands.
This has two benefits: all logic that optimizes for inline constants in
packed math is now in one place; and it applies to both SelectionDAG and
GISel paths.
Disable the use of opsel with v_dot* instructions on gfx11. They are
documented to ignore opsel on src0 and src1. It may be interesting to
re-enable to use of opsel on src2 as a future optimization.
A similar "proper" fix of what inline constants mean could potentially
be applied to unpacked 16-bit ops. However, it's less clear what the
benefit would be, and there are surely places where we'd have to
carefully audit whether values are properly sign- or zero-extended. It
is best to keep such a change separate.
Fixes: Corruption in FSR 2.0 (latent bug exposed by an LLPC change)
