Introduce `OrFail` variants for all MCD Decoder Ops that have
`NumToSKip` encoded with them. This is intended to capture the common
case of jumps to the end of the decoder table which has a `OP_Fail` at
the end. Using the `OrFail` variants of these ops avoid encoding the
`NumToSkip` jump offset for these cases, resulting in a reduction in the
size of the decoder tables (from 5 - 17%). Additionally, for the AArch64
target, the table size reduces enough to switch to using 2-byte
`NumToSkip` encoding instead of existing 3-bytes, resulting in a net 30%
reduction in the size of the decoder table.
The total reduction in the size of the decoder tables for different
targets is as follows (computed using the following command: `for i in
*.inc; do echo -n ``basename $i: ``; grep "MCD::OPC_Fail," $i | awk
'{sum += $2} END { print sum}'; done`)
```
Target Old Size New Size % Reduction
================================================
AArch64 153268 106987 30.20
AMDGPU 412056 340856 17.28
ARC 5061 4605 9.01
ARM 73831 60847 17.59
AVR 1306 1158 11.33
BPF 1927 1795 6.85
CSKY 8692 6922 20.36
Hexagon 41965 34759 17.17
Lanai 982 924 5.91
LoongArch 21629 20035 7.37
M68k 13461 11689 13.16
MSP430 3716 3384 8.93
Mips 31415 25771 17.97
PPC 28931 24771 14.38
RISCV 34800 28352 18.53
Sparc 7432 6236 16.09
SystemZ 32248 29716 7.85
VE 42873 36923 13.88
XCore 2316 2196 5.18
Xtensa 3443 2793 18.88
```
- Add command line option `num-to-skip-size` to parameterize the size of
`NumToSkip` bytes in the decoder table. Default value will be 2, and
targets that need larger size can use 3.
- Keep all existing targets, except AArch64, to use size 2, and change
AArch64 to use size 3 since it run into the "disassembler decoding table
too large" error with size 2.
- Additional fixes on top of earlier revert: mark `decodeNumToSkip` as
static (not necessary anymore as the generated code is now in anonymous
namespace, but doing it for consistency) and incorporate Bazel build
changes from https://github.com/llvm/llvm-project/pull/136212
- Following is a rough reduction in size for the decoder tables by
switching to size 2.
```
Target Old Size New Size % Reduction
================================================
AArch64 153254 153254 0.00
AMDGPU 471566 412805 12.46
ARC 5724 5061 11.58
ARM 84936 73831 13.07
AVR 1497 1306 12.76
BPF 2172 1927 11.28
CSKY 10064 8692 13.63
Hexagon 47967 41965 12.51
Lanai 1108 982 11.37
LoongArch 24446 21621 11.56
MSP430 4200 3716 11.52
Mips 36330 31415 13.53
PPC 31897 28098 11.91
RISCV 37979 32790 13.66
Sparc 8331 7252 12.95
SystemZ 36722 32248 12.18
VE 48296 42873 11.23
XCore 2590 2316 10.58
Xtensa 3827 3316 13.35
```
- Add command line option `num-to-skip-size` to parameterize the size of
`NumToSkip` bytes in the decoder table. Default value will be 2, and
targets that need larger size can use 3.
- Keep all existing targets, except AArch64, to use size 2, and change
AArch64 to use size 3 since it run into the "disassembler decoding table
too large" error with size 2.
- Following is a rough reduction in size for the decoder tables by
switching to size 2.
```
Target Old Size New Size % Reduction
================================================
AArch64 153254 153254 0.00
AMDGPU 471566 412805 12.46
ARC 5724 5061 11.58
ARM 84936 73831 13.07
AVR 1497 1306 12.76
BPF 2172 1927 11.28
CSKY 10064 8692 13.63
Hexagon 47967 41965 12.51
Lanai 1108 982 11.37
LoongArch 24446 21621 11.56
MSP430 4200 3716 11.52
Mips 36330 31415 13.53
PPC 31897 28098 11.91
RISCV 37979 32790 13.66
Sparc 8331 7252 12.95
SystemZ 36722 32248 12.18
VE 48296 42873 11.23
XCore 2590 2316 10.58
Xtensa 3827 3316 13.35
```
The Opcode occupy 2 bytes in following test, we should use {{[0-9]+}}
to match the total value if it, not a part of it.
OPC_Decode(uleb128 Opcode, uleb128 DIdx)
and so do for OPC_TryDecode.
Just like the encoder directive for variable-length instructions, this
patch adds a new decoder directive to allow custom decoder function on
an operand.
Right now, due to the design of DecoderEmitter each operand can only
have a single custom decoder in a given instruction.
Differential Revision: https://reviews.llvm.org/D142079
Currently the DecoderEmitter constructor takes a bunch of string
parameters containing bits of code to interpolate.
However, there's only two ways it can be called. The one used for most
targets which doesn't handle the SoftFail DecoderStatus (not a
problem, because they don't use SoftFail). The other mode, which is
used for ARM/AArch64, does handle SoftFail, but requires an externally
defined helper function in those targets.
This is unnecessary complication; remove the parameters, and unify
onto a single version which does support SoftFail, defining the helper
itself.
To support variable length instructions, I think of them as fixed length instructions with the "maximum length". For example, if there're three instructions with 2, 6 and 9 bytes, we can fit them into the algorithm by treating them all as 9 bytes.
Also, since we can't know the length of the instruction in advance, there is a function object with type `void(APInt &, uint64_t)` added in the parameter list of `decodeInstruction` and `fieldFromInstruction`. We can use this to supply the additional bits the decoder needs after we know the opcode of the instruction.
Finally, `InstrLenTable` is added to let the decoder know the length of the instructions.
See D120960 for its usage.
Reviewed By: myhsu
Differential Revision: https://reviews.llvm.org/D120958
