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Switch refcount of 1 to be isize::MIN as usize

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Also, adds helper methods for inc/dec of refcount.
This commit is contained in:
Brendan Hansknecht 2020-09-26 09:34:21 -07:00
parent 5dc1dace68
commit 3d6d5d1ad0
1 changed files with 29 additions and 69 deletions
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98
compiler/gen/src/llvm/refcounting.rs
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@ -6,6 +6,7 @@ use crate::llvm::build::{
use crate::llvm::build_list::list_len;
use crate::llvm::convert::{basic_type_from_layout, block_of_memory, ptr_int};
use bumpalo::collections::Vec;
use inkwell::basic_block::BasicBlock;
use inkwell::builder::Builder;
use inkwell::context::Context;
use inkwell::module::Linkage;
@ -14,8 +15,7 @@ use inkwell::{AddressSpace, IntPredicate};
use roc_module::symbol::Symbol;
use roc_mono::layout::{Builtin, Layout, MemoryMode};
pub const REFCOUNT_0: usize = std::usize::MAX;
pub const REFCOUNT_1: usize = REFCOUNT_0 - 1;
pub const REFCOUNT_1: usize = isize::MIN as usize;
pub fn decrement_refcount_layout<'a, 'ctx, 'env>(
env: &Env<'a, 'ctx, 'env>,
@ -324,21 +324,8 @@ fn build_inc_list_help<'a, 'ctx, 'env>(
builder.position_at_end(increment_block);
let refcount_ptr = list_get_refcount_ptr(env, layout, original_wrapper);
increment_refcount_help(env, parent, refcount_ptr);
let refcount = env
.builder
.build_load(refcount_ptr, "get_refcount")
.into_int_value();
// our refcount 0 is actually usize::MAX, so incrementing the refcount means decrementing this value.
let decremented = env.builder.build_int_sub(
refcount,
ctx.i64_type().const_int(1 as u64, false),
"incremented_refcount",
);
// Mutate the new array in-place to change the element.
builder.build_store(refcount_ptr, decremented);
builder.build_unconditional_branch(cont_block);
builder.position_at_end(cont_block);
@ -435,51 +422,9 @@ fn build_dec_list_help<'a, 'ctx, 'env>(
builder.build_conditional_branch(is_non_empty, decrement_block, cont_block);
builder.position_at_end(decrement_block);
// build blocks
let then_block = ctx.append_basic_block(parent, "then");
let else_block = ctx.append_basic_block(parent, "else");
let refcount_ptr = list_get_refcount_ptr(env, layout, original_wrapper);
let refcount = env
.builder
.build_load(refcount_ptr, "get_refcount")
.into_int_value();
let comparison = refcount_is_one_comparison(builder, env.context, refcount);
// TODO what would be most optimial for the branch predictor
//
// are most refcounts 1 most of the time? or not?
builder.build_conditional_branch(comparison, then_block, else_block);
// build then block
{
builder.position_at_end(then_block);
if !env.leak {
builder.build_free(refcount_ptr);
}
builder.build_unconditional_branch(cont_block);
}
// build else block
{
builder.position_at_end(else_block);
// our refcount 0 is actually usize::MAX, so decrementing the refcount means incrementing this value.
let decremented = env.builder.build_int_add(
ctx.i64_type().const_int(1 as u64, false),
refcount,
"decremented_refcount",
);
// Mutate the new array in-place to change the element.
builder.build_store(refcount_ptr, decremented);
builder.build_unconditional_branch(cont_block);
}
// emit merge block
builder.position_at_end(cont_block);
decrement_refcount_help(env, parent, refcount_ptr, cont_block);
// this function returns void
builder.build_return(None);
@ -490,25 +435,30 @@ fn increment_refcount_ptr<'a, 'ctx, 'env>(
_parent: FunctionValue<'ctx>,
layout: &Layout<'a>,
field_ptr: PointerValue<'ctx>,
) {
let refcount_ptr = get_refcount_ptr(env, layout, field_ptr);
increment_refcount_help(env, _parent, refcount_ptr);
}
fn increment_refcount_help<'a, 'ctx, 'env>(
env: &Env<'a, 'ctx, 'env>,
_parent: FunctionValue<'ctx>,
refcount_ptr: PointerValue<'ctx>,
) {
let builder = env.builder;
let ctx = env.context;
let refcount_ptr = get_refcount_ptr(env, layout, field_ptr);
let refcount = env
.builder
.build_load(refcount_ptr, "get_refcount")
.into_int_value();
// our refcount 0 is actually usize::MAX, so incrementing the refcount means decrementing this value.
let incremented = env.builder.build_int_sub(
let incremented = env.builder.build_int_add(
refcount,
ctx.i64_type().const_int(1 as u64, false),
"increment_refcount",
);
// Mutate the new array in-place to change the element.
builder.build_store(refcount_ptr, incremented);
}
@ -518,13 +468,23 @@ fn decrement_refcount_ptr<'a, 'ctx, 'env>(
layout: &Layout<'a>,
field_ptr: PointerValue<'ctx>,
) {
let builder = env.builder;
let ctx = env.context;
// the block we'll always jump to when we're done
let cont_block = ctx.append_basic_block(parent, "after_decrement_block");
let refcount_ptr = get_refcount_ptr(env, layout, field_ptr);
decrement_refcount_help(env, parent, refcount_ptr, cont_block);
}
fn decrement_refcount_help<'a, 'ctx, 'env>(
env: &Env<'a, 'ctx, 'env>,
parent: FunctionValue<'ctx>,
refcount_ptr: PointerValue<'ctx>,
cont_block: BasicBlock,
) {
let builder = env.builder;
let ctx = env.context;
let refcount = env
.builder
@ -553,12 +513,12 @@ fn decrement_refcount_ptr<'a, 'ctx, 'env>(
// build else block
{
// TODO: Avoid decrementing if the refcount is 0(read-only/leaked memory)
builder.position_at_end(else_block);
// our refcount 0 is actually usize::MAX, so decrementing the refcount means incrementing this value.
let decremented = env.builder.build_int_add(
ctx.i64_type().const_int(1 as u64, false),
let decremented = env.builder.build_int_sub(
refcount,
"decremented_refcount",
ctx.i64_type().const_int(1 as u64, false),
"decrement_refcount",
);
// Mutate the new array in-place to change the element.