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!fixup lowest_forward_br rename and field docs.

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This commit is contained in:
Jim Posen 2019-07-12 10:39:57 +02:00
parent 93abbcfe56
commit 82bd972333
1 changed files with 12 additions and 9 deletions
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21
src/gas.rs
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@ -42,12 +42,13 @@ pub fn update_call_index(instructions: &mut elements::Instructions, inserted_ind
struct ControlBlock { struct ControlBlock {
/// The lowest control stack index corresponding to a forward jump targeted by a br, br_if, or /// The lowest control stack index corresponding to a forward jump targeted by a br, br_if, or
/// br_table instruction within this control block. The index must refer to a control block /// br_table instruction within this control block. The index must refer to a control block
/// that is not a loop, meaning it is a forward jump. /// that is not a loop, meaning it is a forward jump. Given the way Wasm control flow is
/// structured, the lowest index on the stack represents the furthest forward branch target.
/// ///
/// This value will always be at most the index of the block itself, even if there is no /// This value will always be at most the index of the block itself, even if there is no
/// explicit br instruction targeting this control block. This does not affect how the value is /// explicit br instruction targeting this control block. This does not affect how the value is
/// used in the metering algorithm. /// used in the metering algorithm.
lowest_forward_br: usize, lowest_forward_br_target: usize,
/// The active metering block that new instructions contribute a gas cost towards. /// The active metering block that new instructions contribute a gas cost towards.
active_metered_block: MeteredBlock, active_metered_block: MeteredBlock,
@ -94,7 +95,7 @@ impl Counter {
fn begin_control_block(&mut self, cursor: usize, is_loop: bool) { fn begin_control_block(&mut self, cursor: usize, is_loop: bool) {
let index = self.stack.len(); let index = self.stack.len();
self.stack.push(ControlBlock { self.stack.push(ControlBlock {
lowest_forward_br: index, lowest_forward_br_target: index,
active_metered_block: MeteredBlock { active_metered_block: MeteredBlock {
start_pos: cursor, start_pos: cursor,
cost: 0, cost: 0,
@ -118,17 +119,18 @@ impl Counter {
return Ok(()) return Ok(())
} }
// Update the lowest_forward_br for the control block now on top of the stack. // Update the lowest_forward_br_target for the control block now on top of the stack.
{ {
let control_block = self.stack.last_mut().ok_or_else(|| ())?; let control_block = self.stack.last_mut().ok_or_else(|| ())?;
control_block.lowest_forward_br = min( control_block.lowest_forward_br_target = min(
control_block.lowest_forward_br, closing_control_block.lowest_forward_br control_block.lowest_forward_br_target,
closing_control_block.lowest_forward_br_target
); );
} }
// If there may have been a branch to a lower index, then also finalize the active metered // If there may have been a branch to a lower index, then also finalize the active metered
// block for the previous control block. Otherwise, finalize it and begin a new one. // block for the previous control block. Otherwise, finalize it and begin a new one.
let may_br_out = closing_control_block.lowest_forward_br < closing_control_index; let may_br_out = closing_control_block.lowest_forward_br_target < closing_control_index;
if may_br_out { if may_br_out {
self.finalize_metered_block(cursor)?; self.finalize_metered_block(cursor)?;
} }
@ -180,7 +182,7 @@ impl Counter {
fn branch(&mut self, cursor: usize, indices: &[usize]) -> Result<(), ()> { fn branch(&mut self, cursor: usize, indices: &[usize]) -> Result<(), ()> {
self.finalize_metered_block(cursor)?; self.finalize_metered_block(cursor)?;
// Update the lowest_forward_br of the current control block. // Update the lowest_forward_br_target of the current control block.
for &index in indices { for &index in indices {
let target_is_loop = { let target_is_loop = {
let target_block = self.stack.get(index).ok_or_else(|| ())?; let target_block = self.stack.get(index).ok_or_else(|| ())?;
@ -191,7 +193,8 @@ impl Counter {
} }
let control_block = self.stack.last_mut().ok_or_else(|| ())?; let control_block = self.stack.last_mut().ok_or_else(|| ())?;
control_block.lowest_forward_br = min(control_block.lowest_forward_br, index); control_block.lowest_forward_br_target =
min(control_block.lowest_forward_br_target, index);
} }
Ok(()) Ok(())