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Update DSL docs for cases generator #105753

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Merged
gvanrossum merged 3 commits into from
Jun 14, 2023
Merged

Update DSL docs for cases generator #105753

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8a4ff76
Clarify things around goto error/ERROR_IF a bit
gvanrossum Feb 28, 2023
7f0b623
Remove docs for super-instructions
gvanrossum Jun 13, 2023
732f532
Add pseudo; fix heading markup
gvanrossum Jun 13, 2023
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Remove docs for super-instructions 
Also tweak the text some more.
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@gvanrossum
gvanrossum committed Jun 13, 2023
commit 7f0b62332a189221fde00c53f10c724e3c33ccd5
34 changes: 6 additions & 28 deletions Tools/cases_generator/interpreter_definition.md
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Expand Up @@ -85,8 +85,6 @@ and a piece of C code describing its semantics::
"op" "(" NAME "," stack_effect ")" "{" C-code "}"
|
"macro" "(" NAME ")" "=" uop ("+" uop)* ";"
|
"super" "(" NAME ")" "=" NAME ("+" NAME)* ";"

stack_effect:
"(" [inputs] "--" [outputs] ")"
Expand Down Expand Up @@ -130,8 +128,6 @@ The following definitions may occur:
* `inst`: A normal instruction, as previously defined by `TARGET(NAME)` in `ceval.c`.
* `op`: A part instruction from which macros can be constructed.
* `macro`: A bytecode instruction constructed from ops and cache effects.
* `super`: A super-instruction, such as `LOAD_FAST__LOAD_FAST`, constructed from
normal or macro instructions.

`NAME` can be any ASCII identifier that is a C identifier and not a C or Python keyword.
`foo_1` is legal. `$` is not legal, nor is `struct` or `class`.
Expand Down Expand Up @@ -167,7 +163,7 @@ part of the DSL.
Those functions include:

* `DEOPT_IF(cond, instruction)`. Deoptimize if `cond` is met.
* `ERROR_IF(cond, label)`. Jump to error handler if `cond` is true.
* `ERROR_IF(cond, label)`. Jump to error handler at `label` if `cond` is true.
* `DECREF_INPUTS()`. Generate `Py_DECREF()` calls for the input stack effects.

Note that the use of `DECREF_INPUTS()` is optional -- manual calls
Expand All @@ -193,10 +189,13 @@ These requirements result in the following constraints on the use of
intermediate results.)
3. No `DEOPT_IF` may follow an `ERROR_IF` in the same block.

If an error condition is detected before the first `DECREF` of an input,
(There is some wiggle room: these rules apply to dynamic code paths,
not to static occurrences in the source code.)

If code detects an error condition before the first `DECREF` of an input,
two idioms are valid:

- Just use `goto error`.
- Use `goto error`.
- Use a block containing the appropriate `DECREF` calls ending in
`ERROR_IF(true, error)`.

Expand Down Expand Up @@ -259,27 +258,6 @@ This would generate:
}
```

### Super-instruction definition

```C
super ( LOAD_FAST__LOAD_FAST ) = LOAD_FAST + LOAD_FAST ;
```
This might get translated into the following:
```C
TARGET(LOAD_FAST__LOAD_FAST) {
PyObject *value;
value = frame->f_localsplus[oparg];
Py_INCREF(value);
PUSH(value);
NEXTOPARG();
next_instr++;
value = frame->f_localsplus[oparg];
Py_INCREF(value);
PUSH(value);
DISPATCH();
}
```

### Input stack effect and cache effect
```C
op ( CHECK_OBJECT_TYPE, (owner, type_version/2 -- owner) ) {
Expand Down