[zhoubot]

Summary

Implements the compiler side of PTO-SPEC B.IOT and B.IOS last-use contracts
(PTO-ISA/pto-spec#340) on the
linx_blockisa_llvm_musl release lineage (dev-llvm15_56).

This supersedes #107, which targeted dev-llvm15-v5-encoding. That branch is a
WIP lineage that cannot compile the current SuperNPUBench corpus (it rejects the
BSTART.TLSU TLOAD inline-asm operands used by LinxISA/Linx-TileOP-API), so
the change belongs here instead.

Every B.IOT Local source now carries an independent lifetime decision. A source
written with the .reuse suffix keeps its payload readable after the block; a
source without it is the last architectural payload consumer for the
participating PEs. The encoding stays 32-bit and preserves every existing word.

Field	Change
Two-source Func (14:12)	010 last/last, 011 reuse/last, 111 last/reuse, 100 reuse/reuse (the previous encoding)
One-source Func=101	bit 26: 0 reuse (all pre-change words), 1 last-use; bits 31:27 stay zero
Destination-only Func=110	unchanged
L (19)	still only the effective B.IOT stream terminator, never a lifetime marker

Implementation

• LinxV5RegisterInfo.td: new Tile_{T,U,M,N}OS{1..16}_RU aliases (t#1.reuse, ...)
  and their entries in the tile source register classes so .reuse parses and prints.
• LinxV5InstrInfo.td: four two-source and two one-source lifetime variants; the
  bare-source variants are the new defaults, matching "omission means last-use".
  All existing InstAlias forms are kept, including the tile_t1 absolute spellings.
• LinxV5TRegToOffset.cpp: markTileLastUses freezes each tile source's last-use
  decision from block liveness before operands are rewritten to relative offsets,
  and rewrites retained sources to the _RU alias. A source is last-use when the
  value is neither live out of its block nor read again later in that block.
• LinxV5MCCodeEmitter.cpp / LinxV5TileOpExpand.*: normalizeBIOTLifetimeOpcode
  selects the concrete encoding from the operand .reuse markers at emission time.
• LinxV5AsmParser.cpp: accepts the .reuse tile-register suffix.
• LinxV5Disassembler.cpp: decodes the lifetime forms. The generated decoder only
  covers the non-lifetime variants, so the lifetime fallback rebuilds the operand
  list in the same order and with the same operand decoders as the generated
  decoder (decodePEMode, decodeBIOTDstSizeCode, decodeUImmOperand<1>).

Verification

Toolchain built exactly as SuperNPUBench/README.md prescribes: dev-llvm15_56
plus LinxISA/Linx-TileOP-API @ linx, host-built clang-15 for
linx64v5-unknown-linux-musl.

MC round trip (llvm-mc -show-encoding + llvm-objdump -d), all six lifetime
combinations plus the pre-change words:

B.IOT t#1, mask=1111                  -> 0x04005e13   (bit 26 = last-use)
B.IOT t#1.reuse, mask=1111            -> 0x00005e13   (bit 26 = 0, unchanged)
B.IOT t#1, u#1, mask=1111             -> 0x40002e13   (Func 010)
B.IOT t#1.reuse, u#1, mask=1111       -> 0x40003e13   (Func 011)
B.IOT t#1, u#1.reuse, mask=1111       -> 0x40007e13   (Func 111)
B.IOT t#1.reuse, u#1.reuse, mask=1111 -> 0x40004e13   (Func 100, unchanged)

llvm/test/MC/LinxV5/b.iot.s checks both the encoding and the disassembly of all
those forms (plus the absolute tile_* register spellings); both FileCheck
prefixes pass.

End-to-end on the SuperScalarModel corpus: recompiled SuperNPUBench at revision
78ea4173 (the revision pinned for the SSM release-ops-20260918-repack prebuilt
ELFs) with this toolchain. kernel_matmul_matmul_reuseB_B1_M1024_N1024_K1024_tM128_tN128_tK128
moves from

gfsim: [gfsim] caught std::exception: ASSERTION FAILED: 0 && "Tile register is
not enough for the simulator!"   (prebuilt ELF, all sources reuse/retain)

to

gfrun: R2 = 0 (functional check passes)
gfsim: Total Cycles 719693 (runs to completion)

which is the point of the ISA change: without last-use markers the retained
payload window exhausts the 256 KiB Local pool.

Notes

• -linxv5-reuse-mark is not restored; marking is unconditional because the
  marker is required by the accepted encoding. With the hidden
  -linxv5-enable-reg-to-offset=false MCA mode the _RU rewrite does not run.
• Downstream landing order is PTO-SPEC, LLVM, ASL-MODEL coverage, then the
  SuperScalarModel Phase 2 timing model.

Corpus regeneration with this toolchain

Successive builds of the SuperNPUBench one-level corpus (revision 78ea4173,
the input of the SSM release-ops-20260918-repack prebuilt ELFs) with this
toolchain plus LinxISA/Linx-TileOP-API @ 3be8652 (the pin recorded in the
SuperNPUBench ops-20260918 release notes) and linx64v5-unknown-linux-musl
target:

llvm-lit MC/LinxV5 + CodeGen/LinxV5   base 41 failed -> 39 failed
                                      (b.iot.s and reuse.ll repaired; the
                                       rest are pre-existing SIMT/clang-dependent)
MC lifetime round trip                all six combinations ENC + DIS pass
one-level corpus rebuild              154 ELFs, 21 operators OK
SuperScalarModel gfsim pass list      415 pass / 66 fail  (prebuilt corpus)
                                      429 pass / 52 fail  (regenerated corpus)

The 14 repaired entries are the whole matmul family that used to abort with
Tile register is not enough for the simulator!; they now complete with sane
cycle counts, e.g.

kernel_matmul_matmul_reuseB_B1_M1024_N1024_K1024_tM128_tN128_tK128  719693 cycles
kernel_matmul_matmul_shared_B1_M1024_N1024_K1024_tM128_tN256_tK128  645839 cycles
kernel_matmul_matmul_blockM_B1_M1024_N1024_K1024_tM128_tN128_tK64_bM2_bN1  530988 cycles

Remaining downstream gap

The 52 remaining FA failures are not caused by this change. The released
ops-20260918 / ops-20260922 FA binaries are model-compatible and pass on the
unmodified SuperScalarModel, but they carry no last-use information, so the new
reuse/retain decode makes them exhaust the 256 KiB Local pool. Rebuilding FA with
this public branch tip changes the BSTART.TEPL macro shape (the tip emits an
extra BSTART.TEPL TROWEXPANDEXPDIF header where the released compiler emits a
BSTART.TEPL TMAX header plus a 64-bit TROWEXPANDEXPDIF body), which the
current timing model cannot bind sources to.

The released corpus was built from llvm-project dev-llvm15_56 @ 1037cc1cd
(recorded in the SuperNPUBench release notes and in the ELF .comment). That
commit is no longer reachable in LinxISA/llvm-project (the branch was
force-pushed; gh api .../commits/1037cc1cd returns 422), so the exact FA
codegen cannot be reproduced from public sources. Restoring that revision (or
teaching the model the newer TEPL macro form) closes the FA gap; the B.IOT
markers themselves are already proven on the matmul family.

Shared B.IOS extension (PTO-SPEC llvm#347 / PR llvm#341)

Head: 1f113e161f48adc3507b53c4948feaaf048cbf66.

• Ordinary Shared source: bare Sx encodes bit 26 one (last-use); explicit Sx.reuse encodes bit 26 zero (retained, every old binary word). Destination bit 26 one and bit 27 remain illegal.
• Shared generated pseudos use value/generation-aware liveness, conservatively retaining on CFG uncertainty; MC lowering carries the decision into B.IOS emission. Direct MC, macro parser/folder, disassembler, and Clang integrated assembler agree.
• Public TileOp API inline asm uses %S[Shared]: ordinary Shared inputs print .reuse conservatively, even when the whole INLINEASM operand is killed, because a placeholder may occur multiple times in one template. %K requests one exact textual last-use occurrence and fails closed unless the operand is a killed pure input; %R explicitly retains a tied source. Generated pseudos still emit last-use automatically. Existing API wrappers have not been annotated with %K, so their Shared sources will remain retained until a call-site-safe API change; the regenerated corpus must be counted before performance claims.
• Local markTileLastUses now excludes INLINEASM regdef operands from kill mutation; assertions-on Clang previously crashed on tscatter_fp32_16x16, and the exact compile plus a minimal MIR regression now pass.
• Focused Local/Shared MC/CodeGen suite: 10/10 PASS, including encoding/disassembly, destination negatives, repeated placeholders, tied operands, loop backedges, live-after %K rejection, and INLINEASM regdef. Clang integrated assembler passed; git diff --check and changed-line clang-format passed. Broader LinxV5 suite before the final small crash fix: 150 PASS, 1 XFAIL, 31 pre-existing/tool-availability failures (not treated as a clean suite).
• Full reproducible SuperNPUBench source corpus was rebuilt from e74884e using assertions-on Clang at this exact head and the pinned Linx musl/libc++ sysroot: 614 unique ELF files (424 micro, 190 one-level), with all 5 micro and all 29 one-level build scripts attempted. Source-path list matches the prior 614 corpus exactly. Successful and failing family status is explicit in the report; not every source variant compiled successfully.
• Disassembly of all 614 ELFs finds 23,770 ordinary B.IOS Shared sources, all .reuse and zero last-use. This is correct fail-safe behavior for the unannotated public TileOp API inline-asm wrappers, but this corpus cannot measure Shared early-release benefit. Compiler-generated Shared pseudos and explicit %K can emit bit26=1, as the focused tests show. ELF list, SHA-256 manifest, per-family logs, and marker census: /Users/zhoubot/.codex/artifacts/bios-last-use-corpus-20260923/.

[zhoubot]

Independent exact-head re-review completed for fa76e69656fa against dev-llvm15_56@66816b2b5178: APPROVE, zero findings. The amended head fixes all five prior review findings: destination-bearing source operand indices, retain preservation when relative rewriting is disabled/untracked, invalid zero-size destination shorthand, reserved one-source bits [31:27], and TileOp macro folding for all lifetime opcodes. Fresh llvm-mc/llvm-objdump/llc rebuild passed; six targeted lit tests and the expanded 18-test B.IOT/macro suite passed; git diff --check is clean.

[VV0003]

This PR is superseded by the implementation already present on dev-llvm15_56.

The three changes are now in the target branch as:

• cf2cbb28d013 — B.IOT source last-use markers
• a851da05c1ae — B.IOS Shared source lifetime
• 782630815dce — ignore inline-asm defs in tile last-use marking

The current branch also contains follow-up fixes for masked Tile/lifetime interaction (96b42963282b) and the final PR #131 ISA/regression fixes (47557a08c4b5).

Validation against the current target build (/tmp/linx-llvm-pr131-rebased-build, assertions enabled):

• B.IOT/B.IOS MC lifetime tests
• Local/Shared reuse and cross-block codegen tests
• inline-asm last-use negative/modifier tests
• Shared register allocation and inline-asm-def MIR regression

Result: 9/9 PASS. No additional code from this historical PR should be merged; closing as superseded.