Optimize V_SET_INACTIVE by allow it to run in WWM.
Hence WWM sections are not broken up for inactive lane setting.
WWM V_SET_INACTIVE can typically be lower to V_CNDMASK.
Some cases require use of exec manipulation V_MOV as previous code.
GFX9 sees slight instruction count increase in edge cases due to
smaller constant bus.
Additionally avoid introducing exec manipulation and V_MOVs where
a source of V_SET_INACTIVE is the destination.
This is a common pattern as WWM register pre-allocation often
assigns the same register.
At the moment, the emergency spill slot is a fixed object for entry
functions and chain functions, and a regular stack object otherwise.
This patch adopts the latter behaviour for entry/chain functions too. It
seems this was always the intention [1] and it will also save us a bit
of stack space in cases where the first stack object has a large
alignment.
[1]
34c8b835b1
Switch to using immediate offsets instead of the SP register to access
objects on the current stack frame in chain functions. This means we no
longer need to reserve a SP register just for accesing stack objects and
it also allows us to set the SP (when one is actually needed) to the
stack size from the very beginning.
This only works if we use a FixedObject for the ScavengeFI, which is
what we do for entry functions anyway (and we generally want to keep
chain functions close to amdgpu_cs behaviour where we don't have a good
reason to diverge).
Initialize the SP to 0 in the prologue of functions with the
`amdgpu_cs_chain` or `amdgpu_cs_chain_preserve` calling conventions, but
only if they need one (i.e. if they contain calls to `amdgpu_gfx`
functions or if they have stack objects).
Also make sure we don't try to realign the stack (since 0 is aligned
enough).
Differential Revision: https://reviews.llvm.org/D156413
Teach prolog epilog insertion how to handle functions with the
amdgpu_cs_chain or amdgpu_cs_chain_preserve calling conventions.
For amdgpu_cs_chain functions, we only need to preserve the inactive
lanes of VGPRs above v8, and only in the presence of calls via
@llvm.amdgcn.cs.chain.
For amdgpu_cs_chain_preserve functions, we will also need to preserve
the active lanes for registers above the last argument VGPR. AFAICT
there's no direct way to find out what the last argument VGPR is, so
instead the patch uses the fact that chain calls from
amdgpu_cs_chain_preserve functions can't use more VGPRs than the
caller's VGPR arguments. In other words, it removes the operands of
SI_CS_CHAIN_TC instructions from the list of callee saved registers.
For both calling conventions, registers v0-v7 never need to be saved and
restored, so we should never add them as WWM spills.
Differential Revision: https://reviews.llvm.org/D156412
The @llvm.amdgcn.cs.chain intrinsic is essentially a call. The call
parameters are bundled up into 2 intrinsic arguments, one for those that
should go in the SGPRs (the 3rd intrinsic argument), and one for those
that should go in the VGPRs (the 4th intrinsic argument). Both will
often be some kind of aggregate.
Both instruction selection frameworks have some internal representation
for intrinsics (G_INTRINSIC[_WITH_SIDE_EFFECTS] for GlobalISel,
ISD::INTRINSIC_[VOID|WITH_CHAIN] for DAGISel), but we can't use those
because aggregates are dissolved very early on during ISel and we'd lose
the inreg information. Therefore, this patch shortcircuits both the
IRTranslator and SelectionDAGBuilder to lower this intrinsic as a call
from the very start. It tries to use the existing infrastructure as much
as possible, by calling into the code for lowering tail calls.
This has already gone through a few rounds of review in Phab:
Differential Revision: https://reviews.llvm.org/D153761
Lower formal arguments and returns for functions with the
`amdgpu_cs_chain` and `amdgpu_cs_chain_preserve` calling conventions:
* Put `inreg` arguments into SGPRs, starting at s0, and other arguments
into VGPRs, starting at v8. No arguments should end up on the stack, if
we don't have enough registers we should error out.
* Lower the return (which is always void) as an S_ENDPGM.
* Set the ScratchRSrc register to s48:51, as described in the docs.
* Set the SP to s32, matching amdgpu_gfx. This might be revisited in a
future patch.
Differential Revision: https://reviews.llvm.org/D153517
