[RISCV] Enable bidirectional scheduling and tracking register pressure (#115445)


This is based on other targets like PPC/AArch64 and some experiments.

This PR will only enable bidirectional schedu

[RISCV] Enable bidirectional scheduling and tracking register pressure (#115445)


This is based on other targets like PPC/AArch64 and some experiments.

This PR will only enable bidirectional scheduling and tracking register
pressure.

Disclaimer: I haven't tested it on many cores, maybe we should make
some options being features. I believe downstreams must have tried
this before, so feedbacks are welcome.

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[RISCV] Enable load clustering by default (#73789)

We believe this is neutral or slightly better in the majority of cases.

[RISCV] Mark Zacas as non-experimental (#109651)

The extension has been ratified for some time, but we kept it
experimental (see #99898) due to
<https://github.com/riscv-non-isa/riscv-elf-psabi-do

[RISCV] Mark Zacas as non-experimental (#109651)

The extension has been ratified for some time, but we kept it
experimental (see #99898) due to
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/444>. The
ABI issue has been resolved by #101023 so I believe there's no known
barrier to moving Zacas to non-experimental.

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[RISCV] Add additional fence for amocas when required by recent ABI change (#101023)

A recent atomics ABI change / fix requires that for the "A6C" and A6S"
atomics ABIs (i.e. both of those supporte

[RISCV] Add additional fence for amocas when required by recent ABI change (#101023)

A recent atomics ABI change / fix requires that for the "A6C" and A6S"
atomics ABIs (i.e. both of those supported by LLVM currently), an
additional fence is inserted for an atomic_compare_exchange with seq_cst
failure ordering.
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/445>

This isn't trivial to support through the hooks used by AtomicExpandPass
because that pass assumes that when fences are inserted, the original
atomics ordering information can be removed from the instruction. Rather
than try to change and complicate that API, this patch implements the
needed fence insertion through a small special purpose pass.

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[RISCV] Mark zacas as experimental again due to unresolved ABI issue (#99898)

As discussed at the last sync-up call, mark Zacas as experimental until
this ABI issue is resolved
<https://github.com

[RISCV] Mark zacas as experimental again due to unresolved ABI issue (#99898)

As discussed at the last sync-up call, mark Zacas as experimental until
this ABI issue is resolved
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/444>.

Don't return Zacas in getHostCPUFeatures (leaving a TODO there) as even if requesting detection of "native" features, the user likely doesn't want to automatically opt in to experimental codegen.

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AtomicExpand: Emit or with constant on RHS

This will save later code from commuting it.

[RISCV] Remove experimental from Zacas. (#83195)

Document that we don't use the double compare and swap instructions due
to ABI concerns.

[RISCV] Use Zacas for AtomicRMWInst::Nand i32 and XLen. (#80119)

We don't have an AMO instruction for Nand, so with the A extension we
use an LR/SC loop. If we have Zacas we can use a CAS loop inst

[RISCV] Use Zacas for AtomicRMWInst::Nand i32 and XLen. (#80119)

We don't have an AMO instruction for Nand, so with the A extension we
use an LR/SC loop. If we have Zacas we can use a CAS loop instead.

According to the Zacas spec, a CAS loop scales to highly parallel
systems better than LR/SC.

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[RISCV] Add IsSignExtendingOpW to amocas.w. (#79351)

[RISCV] Add test cases showing missed opportunity to remove sext.w after amocas.w. NFC

[RISCV] Omit "@plt" in assembly output "call foo@plt" (#72467)

R_RISCV_CALL/R_RISCV_CALL_PLT distinction is not necessary and
R_RISCV_CALL has been deprecated. Since https://reviews.llvm.org/D132530

[RISCV] Omit "@plt" in assembly output "call foo@plt" (#72467)

R_RISCV_CALL/R_RISCV_CALL_PLT distinction is not necessary and
R_RISCV_CALL has been deprecated. Since https://reviews.llvm.org/D132530
`call foo` assembles to R_RISCV_CALL_PLT. The `@plt` suffix is not
useful and can be removed now (matching AArch64 and PowerPC).

GNU assembler assembles `call foo` to RISCV_CALL_PLT since 2022-09
(70f35d72ef04cd23771875c1661c9975044a749c).

Without this patch, unconditionally changing MO_CALL to MO_PLT could
create `jump .L1@plt, a0`, which is invalid in LLVM integrated assembler
and GNU assembler.

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[RISCV] Add IsSignExtendingOpW to AMO*_W instructions. (#72349)

[RISCV] Add test cases showing missed opportunity to remove sext.w after amo*.w. NFC

We should tell RISCVOptWInstrs that these instructions sign extend
their results.

[RISCV] Strip W suffix from ADDIW (#68425)

The motivation of this change is simply to reduce test duplication. As
can be seen in the (massive) test delta, we have many tests whose output
differ on

[RISCV] Strip W suffix from ADDIW (#68425)

The motivation of this change is simply to reduce test duplication. As
can be seen in the (massive) test delta, we have many tests whose output
differ only due to the use of addi on rv32 vs addiw on rv64 when the
high bits are don't care.

As an aside, we don't need to worry about the non-zero immediate
restriction on the compressed variants because we're not directly
forming the compressed variants. If we happen to get a zero immediate
for the ADDI, then either a later optimization will strip the useless
instruction or the encoder is responsible for not compressing the
instruction.

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[RISCV] Add simple DAG combine to pull xor with 1 through select_cc.

If we're selecting the result of two setccs that have been legalized
by introducing an xor with 1, we can pull the xor with 1 thr

[RISCV] Add simple DAG combine to pull xor with 1 through select_cc.

If we're selecting the result of two setccs that have been legalized
by introducing an xor with 1, we can pull the xor with 1 through the
select to enable more optimizations.

We could generalize this to other binary operators with identical
conditions, but those are usually caught before we legalize the select.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D156144

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[RISCV] Use LBU for extloadi8.

The Zcb extension has c.lbu, but not c.lb. This patch makes us
prefer LBU over LB if we have a choice which will enable more
compression opportunities.

Reviewed By: a

[RISCV] Use LBU for extloadi8.

The Zcb extension has c.lbu, but not c.lb. This patch makes us
prefer LBU over LB if we have a choice which will enable more
compression opportunities.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D146270

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[RISCV] Add pass to remove W suffix from ADDIW and SLLIW to improve compressibility

SLLI and ADD are more compressible than SLLIW and ADDW. SLLI/ADD both have a 5-bit register encoding. SLLIW/ADDW h

[RISCV] Add pass to remove W suffix from ADDIW and SLLIW to improve compressibility

SLLI and ADD are more compressible than SLLIW and ADDW. SLLI/ADD both have a 5-bit register encoding. SLLIW/ADDW have a 3-bit register encoding. They both require the dest to also be one of the sources.

We aggressively form ADDW/SLLIW as it helps hasAllWBitUsers in RISCVISelDAGToDAG to not require recursion. So we need a pass to remove excessive -w suffixes.

Differential Revision: https://reviews.llvm.org/D139948

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[RISCV] Convert some tests to opaque pointers (NFC)

[RISCV] Add ADDW/AND/OR/XOR/SUB/SUBW to getRegAllocHints.

These instructions requires both register operands to be compressible
so I've only applied the hint if we already have a GPRC physical regis

[RISCV] Add ADDW/AND/OR/XOR/SUB/SUBW to getRegAllocHints.

These instructions requires both register operands to be compressible
so I've only applied the hint if we already have a GPRC physical register
assigned for the other register operand.

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D139079

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[RISCV] Teach getRegAllocationHints about compressible SRAI/SRLI.

Similar to previous patches for ADDI/ADDIW/SLLI/ADD, but restricted
to only cases where the register is x8-x15(GPRC reg class).

I'v

[RISCV] Teach getRegAllocationHints about compressible SRAI/SRLI.

Similar to previous patches for ADDI/ADDIW/SLLI/ADD, but restricted
to only cases where the register is x8-x15(GPRC reg class).

I've restricted it so that we can be precise about whether the
resulting instruction would be compressible. Changing the register
allocation may make some other instruction not compressible so we
should try to be accurate.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D138740

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[RISCV] Use register allocation hints to improve use of compressed instructions.

Compressed instructions usually require one of the source registers
to also be the source register. The register allo

[RISCV] Use register allocation hints to improve use of compressed instructions.

Compressed instructions usually require one of the source registers
to also be the source register. The register allocator doesn't have
that bias on its own.

This patch adds register allocation hints to introduce this bias.
I've started with ADDI, ADDIW, and SLLI. These all have a 5-bit
field for the register. If the source and dest register are the
same they are guaranteed to compress as long as the immediate is
also 6 bits.

This code was inspired by similar code from the SystemZ target.

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D138242

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[RISCV] Teach ComputeNumSignBitsForTargetNode about masked atomic intrinsics

An unnecessary sext.w is generated when masking the result of the
riscv_masked_cmpxchg_i64 intrinsic. Implementing handli

[RISCV] Teach ComputeNumSignBitsForTargetNode about masked atomic intrinsics

An unnecessary sext.w is generated when masking the result of the
riscv_masked_cmpxchg_i64 intrinsic. Implementing handling of the
intrinsic in ComputeNumSignBitsForTargetNode allows it to be removed.

Although this isn't a particularly important optimisation, removing the
sext.w simplifies implementation of an additional cmpxchg-related
optimisation in D130192.

Although I can't produce a test with different codegen for the other
atomics intrinsics, these are added as well for completeness.

Differential Revision: https://reviews.llvm.org/D130191

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[RISCV][test] Add tests showing signext behaviour of cmpxchg

[SDAG] try to replace subtract-from-constant with xor

This is almost the same as the abandoned D48529, but it
allows splat vector constants too.

This replaces the x86-specific code that was added w

[SDAG] try to replace subtract-from-constant with xor

This is almost the same as the abandoned D48529, but it
allows splat vector constants too.

This replaces the x86-specific code that was added with
the alternate patch D48557 with the original generic
combine.

This transform is a less restricted form of an existing
InstCombine and the proposed SDAG equivalent for that
in D128080:
https://alive2.llvm.org/ce/z/OUm6N_

Differential Revision: https://reviews.llvm.org/D128123

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[RISCV] Set CostPerUse to 1 iff RVC is enabled

After D86836, we can define multiple cost values for
different cost models. So here we set CostPerUse to
1 iff RVC is enabled to avoid potential impact

[RISCV] Set CostPerUse to 1 iff RVC is enabled

After D86836, we can define multiple cost values for
different cost models. So here we set CostPerUse to
1 iff RVC is enabled to avoid potential impact on RA.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D117741

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