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docs: Split ssa_versions[]

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Signed-off-by: Ronald Caesar <github43132@proton.me>
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Ronald Caesar
2026-01-08 19:19:19 -04:00
parent f97fcf7df9
commit 2778c94a15
1 changed files with 9 additions and 26 deletions
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docs/IR_DESIGN_DOC.md
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@@ -20,13 +20,8 @@ typedef struct
source_variable_t source_variables[???];
typedef struct
{
uint8_t bit_width; // 8/16/32/64.
uint16_t use_count;
} ssa_version_t;
ssa_version_t ssa_versions[???];
uint8_t ssa_bit_widths[???]; // 8/16/32/64/etc.
uint16_t ssa_use_counts[???];
```
## Constants
@@ -53,17 +48,18 @@ uint32_t instruction_count;
### Encoding Symbols
<**src3**> 17-bit index for `ssa_versions[]`.
<**src3**> 17-bit index for `ssa` arrays.
<**src2**> 17-bit index for `ssa_versions[]`.
<**src2**> 17-bit index for `ssa` arrays.
<**src1**> 17-bit index for `ssa_versions[]`.
<**src1**> 17-bit index for `ssa` arrays.
<**opc**> 11-bit opcode.
### Operational Information
If Bit[16] in `src1`, `src2`, or `src` is 1, the operand is a index into `constant_pool[]`. It has no SSA index. It has no entry in `ssa_versions`.
If Bit[16] in `src1`, `src2`, or `src` is 1, the operand is a index into
`constant_pool[]`. It has no SSA index. It has no entry in `ssa` arrays.
## Block Scope
@@ -336,12 +332,7 @@ You can **only** change an instruction to `OPCODE_NOP` to kill it.
### Rule 3.1: Typed Definitions
The type of a variable is defined only in `ssa_versions[]`. Instructions that
**use** variables do not encode the expected type.
This reduces opcode density. `OPCODE_ADD` doesnt need to say `OPCODE_ADD_INT32`.
It just says `OPCODE_ADD v1, v2`. Ballistic will look up `v1`'s type. If `v1`
and is a float and `v2` is int, Ballistic throws an error.
The type of a variable is defined by the opcode.
### Rule 3.2: Void Type
@@ -686,18 +677,10 @@ OPCODE_RETURN v14
We use **Implicit Indexing**:
1. When we create an instruction at `instructions[100]`, we have implicitly
created the variable definition at `ssa_versions[100]`.
created the variable definition in ssa arrays such as `ssa_types[]`.
2. We do not "check" if it is created. The act of incrementing
`instruction_count` creates it.
This removes the need for an explicit `definition` bitfield in
`instructions_t`, creating space to expand `src1`, `src2`, and `src3` to 18
bits.
## What about instructions that don't define anything?
If `instructions[200]` is `STORE v1, [v2]`, it defines no variable for other
instructions to use. If we strictly follow implicit indexing, we create
`ssa_values[200]`. We handle these void instructions by marking the SSA
variable as `VOID`: `ssa_versions[200].type = TYPE_VOID`.