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Add MC support for CHERI memory colouring instructions. #508

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Add MC support for CHERI memory colouring instructions. #508

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c23f037
Add MC support for CHERI memory colouring instructions.
davidchisnall Jan 28, 2021
8c1b90c
Disable CHERI memory colouring instructions by default.
davidchisnall Jan 29, 2021
423b758
Updates to memory versioning instructions.
ronorton Mar 17, 2021
40de332
Minor formatting changes requested by jrtc27.
ronorton Mar 17, 2021
ee5ab1b
Add brackets around memory operand for cloadversion(s), cstoreversion…
ronorton Mar 17, 2021
2abcb04
Change encoding of cloadversion after jalr.pcc was accidentally alloc…
ronorton Jun 16, 2021
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18 changes: 18 additions & 0 deletions llvm/lib/Target/RISCV/RISCVInstrInfoXCheri.td
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Original file line number Diff line number Diff line change
Expand Up @@ -1554,3 +1554,21 @@ let Predicates = [HasCheri, IsRV64, IsCapMode] in {
defm : CheriLdPat<load, CLC_128>;
defm : CheriStPat<store, CSC_128, GPCR>;
} // Predicates = [HasCheri, IsRV64, IsCapMode]


/// CHERI memory colouring extensions
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Instructions go in the first half of the file to keep MC and CodeGen cleanly separated*

(* pseudos are more complicated, but placed based on whether they're used for assembly or just CodeGen)

let Predicates = [HasCheri, IsRV64] in {
def CGetVersion : Cheri_r<0x13, "cgetversion">;
def CSetVersion : Cheri_rr<0x2, "csetversion">;
let mayLoad = 1 in
{
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def CLoadVersion : Cheri_r<0x14, "cloadversion">;
def CLoadVersions : Cheri_r<0x15, "cloadversions">;
}
let mayStore = 1, mayLoad = 0, hasSideEffects = 0 in
def CStoreVersion : RVInstCheriTwoSrc<0x7e, 0x2, 0, OPC_CHERI, (outs),
(ins GPR:$rs1, GPCR:$rs2),
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"cstoreversion", "$rs1, $rs2">;
let mayLoad = 1, mayStore = 1 in
def CAmoCDecVersion : Cheri_rr<0x3, "camocdecversion", GPR>;
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Is it important to indicate that $rs1 is atomic?

Suggested change
def CAmoCDecVersion : Cheri_rr<0x3, "camocdecversion", GPR>;
def CAmoCDecVersion : Cheri_rr<0x3, "camocdecversion", GPR, GPR, GPCRMemAtomic>;

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@arichardson arichardson Jan 28, 2021 •
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I believe that type exists only to allow using 0(ca0) in the assembler despite the instruction not having an immediate operand.

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I've not seen that before, but in other back ends you never specify anything explicitly on operands to indicate that they are the memory addresses for atomics.

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Yes it's solely a parser thing. RISC-V's atomic operands are the only memory-accessing instructions that don't take an immediate, and have (rs1) as the canonical form but also accept 0(rs1), primarily to make it easy for generated assembly. Since our explicit loads and stores end up looking the same in terms of operands I reused the existing class (and its corresponding capability version), and did not rename it to avoid merge conflicts just for something cosmetic. In this case you do want the suggested change, but only so its assembly syntax matches the other AMOs, i.e. that 0(cs1) is permitted in the assembly.

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This being the case I am tempted to (ab)use GPCRMemAtomic for the address operands to cloadversion and cstore version too so that they get brackets around the address. Thoughts?

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Yeah, that's what I would do, then it matches the explicit loads/stores. Maybe one day I'll rename it to something more general (and do so upstream too, even if it currently makes less sense, but I think the hypervisor load/store-as-guest instructions are also immediate-less and will end up wanting the same syntax).

}
23 changes: 23 additions & 0 deletions llvm/test/MC/RISCV/cheri/rv64xcheri-version.s
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@@ -0,0 +1,23 @@
# RUN: llvm-mc %s -triple=riscv64 -mattr=+xcheri -show-encoding \
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These belong in rv64xcheri-valid.s as it stands

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(though a separate extension means rv64xname-valid.s for some other name)

# RUN: | FileCheck %s

# CHECK: cgetversion gp, csp
# CHECK: encoding: [0xdb,0x01,0x31,0xff]
CGetVersion x3, c2
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# CHECK: csetversion cra, csp, gp
# CHECK: encoding: [0xdb,0x00,0x31,0x04]
CSetVersion c1, c2, x3
# CHECK: cloadversion sp, cra
# CHECK: encoding: [0x5b,0x81,0x40,0xff]
CloadVersion x2, c1
# CHECK: cloadversions sp, cra
# CHECK: encoding: [0x5b,0x81,0x50,0xff]
CloadVersions x2, c1
# CHECK: cstoreversion ra, ctp
# CHECK: encoding: [0x5b,0x81,0x40,0xfc]
CStoreVersion x1, c4
# CHECK: camocdecversion ra, csp, gp
# CHECK: encoding: [0xdb,0x00,0x31,0x06]
CAmoCDecVersion x1, c2, x3