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docs: Aggressively packed instruction struct

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Signed-off-by: Ronald Caesar <github43132@proton.me>
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Ronald Caesar
2025-12-25 02:53:06 -04:00
parent 752a708bd8
commit 780b884d35
1 changed files with 35 additions and 24 deletions
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59
src/IR_DESIGN_DOC.md
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@@ -102,21 +102,6 @@ uint32_t phi_operand_pool[???];
## Instruction Design
```c
// Strict 16-byte alignment
typedef struct
{
uint16_t opcode;
// See Section `Instruction Flags Design` for encoding layout.
uint16_t flags;
// SSA versions
// x3 = y1 + z2
uint32_t definition; // x3
uint32_t operand1; // y1
uint32_t operand2; // z2
} instruction_t;
// An example of how variable renaming should work. This does not apply to
// constants. We will focus on the variable `a`. Lets assume variable `a` is
// stored in original_variables[5].
@@ -127,11 +112,42 @@ typedef struct
// ssa_versions[1].original_variable_id = 5;
//
// 20: b1 = a1 + ???;
// instructions[20].operand1 = original_variables[5].reaching_definition;
// instructions[20].source1= original_variables[5].reaching_definition;
//
// 30: c1 = a1 + b1;
// instructions[30].operand1 = original_variables[5].reaching_definition;
instruction_t instructions[???];
// instructions[30].source1 = original_variables[5].reaching_definition;
// Strict 8-byte alignment
typedef struct
{
// 64 Opcodes
unsigned int opcode: 6;
// See Section `Instruction Flags Design` for encoding layout.
uint16_t flags;
// 0-16383
unsigned int definition: 14;
unsigned int source1: 14;
unsigned int source2: 14;
} instruction_t;
// Use when variables or constants > 16383
typedef struct
{
uint32_t definition;
uint32_t source1;
uint32_t source2;
uint32_t _padding;
} large_instruction_t
instruction_t instructions[???]; // High Density
large_instruction_t large_instructions[???]; // Low Density
// Extension Handling
#define IR_GET_LARGE_INDEX(i) ((i) & 0xFFFFFFF) // 42 bits
```
## Instruction Flags Design
@@ -234,12 +250,7 @@ E Condition Width Global Flags
### 4. Extention Flag Bit[15]
This is for rare instructions like `MADD` which has 3 variable arguments while `instruction_t` only supports 2.
1. If Instruction.E = 1, the **next** 16-byte slot in the instructions array is *not* an instruction.
2. It treats that next slot as a data container to retrieve the 3rd operand.
3. The iterator increments by 2 instead of 1.
This is for constants and variables greater than 16383.
### 5. Access Macros