From b84509c938fb18db3985944a98822b3176920ec3 Mon Sep 17 00:00:00 2001 From: Chris Fallin Date: Sat, 20 Nov 2021 01:29:46 -0800 Subject: [PATCH] WIP. --- src/backend.rs | 155 +++++++++++++++++++++++++++++++++++++++++++++---- src/cfg/mod.rs | 8 +++ src/ir.rs | 13 ++++- 3 files changed, 164 insertions(+), 12 deletions(-) diff --git a/src/backend.rs b/src/backend.rs index aae9aa7..97466df 100644 --- a/src/backend.rs +++ b/src/backend.rs @@ -7,31 +7,166 @@ pub enum Shape { Block { head: BlockId, children: Vec }, Loop { head: BlockId, children: Vec }, Leaf { block: BlockId, succs: Vec }, + None, } +/// Index in RPO. +type OrderedBlockId = usize; + +#[derive(Clone, Copy, Debug)] enum Region { /// Forward-branch region. Extends from end (just prior to /// terminator) of first block to just before second block. Can be /// extended earlier, prior to the beginning, if needed. - Forward(BlockId, BlockId), + Forward(OrderedBlockId, OrderedBlockId), /// Backward-branch region. Extends from start of first block to /// end (after terminator) of second block. Can be extended past - /// the end if needed. TODO: actually record all jump-points. - Backward(BlockId, BlockId), + /// the end if needed. + Backward(OrderedBlockId, OrderedBlockId), +} + +#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)] +struct RegionEndpoint { + block: OrderedBlockId, + pt: BlockPoint, +} + +impl RegionEndpoint { + fn start(block: OrderedBlockId) -> Self { + RegionEndpoint { + block, + pt: BlockPoint::Start, + } + } + fn end(block: OrderedBlockId) -> Self { + RegionEndpoint { + block, + pt: BlockPoint::Start, + } + } +} + +#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)] +enum BlockPoint { + Start, + End, +} + +impl Region { + fn start(&self) -> RegionEndpoint { + match self { + &Region::Forward(a, _) => RegionEndpoint::end(a), + &Region::Backward(a, _) => RegionEndpoint::start(a), + } + } + + fn end(&self) -> RegionEndpoint { + match self { + &Region::Forward(_, b) => RegionEndpoint::start(b), + &Region::Backward(_, b) => RegionEndpoint::end(b), + } + } + + fn contains(&self, other: &Region) -> bool { + self.start() <= other.start() && self.end() >= other.end() + } + + fn overlaps(&self, other: &Region) -> bool { + self.end() >= other.start() && other.end() >= self.start() + } } impl Shape { - pub fn compute(f: &FunctionBody, cfg: &CFGInfo) -> Self { + pub fn compute(_f: &FunctionBody, cfg: &CFGInfo) -> Self { // Process all non-contiguous edges in RPO block order. For // forward and backward edges, emit Regions. + let order = cfg.rpo(); + assert_eq!(order[0], 0); // Entry block should come first. + let mut regions = vec![]; + for (block_pos, &block) in order.iter().enumerate() { + for &succ in cfg.succs(block) { + let succ_pos = cfg + .rpo_pos(succ) + .expect("if block is reachable then succ should be too"); + if succ_pos < block_pos { + regions.push(Region::Backward(succ_pos, block_pos)); + } else if succ_pos > block_pos + 1 { + regions.push(Region::Forward(block_pos, succ_pos)); + } + } + } - // Sort regions by start. Then examine adjacent regions to - // resolve nesting. If out-of-order, we can extend a Forward - // region's start backward, or a Backward region's end - // forward. If still out-of-order, drop any conflicting - // Backward; we'll handle by duplication. + // Initially sort regions by start pos to get them in rough + // order; we'll resolve exact ordering below by extending + // regions where necessary and duplicating where we find + // irreducible control flow. + regions.sort_by_key(|r| r.start()); - todo!() + // Examine each region in the sequence, determining whether it + // is properly nested with respect to all overlapping regions. + let mut i = 0; + while i + 1 < regions.len() { + i += 1; + let prev = regions[i - 1]; + let this = regions[i]; + + if !prev.overlaps(&this) { + continue; + } + + match (prev, this) { + (Region::Backward(a, b), Region::Backward(c, d)) if a == c => { + // Merge by extending end. + regions[i - 1] = Region::Backward(a, std::cmp::max(b, d)); + regions.remove(i); + } + (Region::Backward(a, b), Region::Backward(c, _d)) if a < c && c <= b => { + panic!("Irreducible CFG"); + } + (Region::Backward(a, b), Region::Forward(c, d)) if a <= c && c <= b => { + // Put the Forward before the Backward (extend its + // start) to ensure proper nesting. + regions[i - 1] = Region::Forward(a, d); + regions[i] = Region::Backward(a, b); + } + (Region::Forward(_a, b), Region::Backward(c, d)) if b > c && b <= d => { + panic!("Irreducible CFG"); + } + (Region::Forward(a, b), Region::Forward(c, d)) if b == d => { + // Merge. + regions[i - 1] = Region::Forward(std::cmp::min(a, c), b); + regions.remove(i); + } + (Region::Forward(a, b), Region::Forward(c, d)) if a <= c && b < d => { + regions[i - 1] = Region::Forward(a, d); + regions[i] = Region::Forward(a, b); + } + _ => {} + } + } + + // Ensure the regions properly nest. + let mut stack: Vec = vec![]; + for region in ®ions { + while let Some(top) = stack.last() { + if top.contains(region) { + stack.push(region.clone()); + break; + } else if region.contains(top) { + stack.pop(); + } else if region.overlaps(top) { + panic!( + "Non-nested region: {:?} in nest: {:?} (overall: {:?})", + region, stack, regions + ); + } + } + if stack.is_empty() { + stack.push(region.clone()); + } + } + + Shape::None } } diff --git a/src/cfg/mod.rs b/src/cfg/mod.rs index 898faa8..f0359a0 100644 --- a/src/cfg/mod.rs +++ b/src/cfg/mod.rs @@ -88,4 +88,12 @@ impl CFGInfo { let is_return = self.return_blocks.binary_search(&block).is_ok(); self.succs(block).len() + if is_return { 1 } else { 0 } } + + pub fn rpo(&self) -> Vec { + self.postorder.iter().cloned().rev().collect() + } + + pub fn rpo_pos(&self, block: BlockId) -> Option { + self.postorder_pos[block].map(|fwd_pos| self.postorder.len() - 1 - fwd_pos) + } } diff --git a/src/ir.rs b/src/ir.rs index 41275d5..ca64f3e 100644 --- a/src/ir.rs +++ b/src/ir.rs @@ -1,6 +1,6 @@ //! Intermediate representation for Wasm. -use crate::{backend, frontend}; +use crate::{backend::Shape, cfg::CFGInfo, frontend}; use anyhow::Result; use wasmparser::{FuncType, Operator, Type}; @@ -210,7 +210,16 @@ impl<'a> Module<'a> { frontend::wasm_to_ir(bytes) } - pub fn to_wasm_bytes(mut self) -> Vec { + pub fn to_wasm_bytes(self) -> Vec { + for func in &self.funcs { + match func { + &FuncDecl::Body(_, ref body) => { + let cfg = CFGInfo::new(body); + let _shape = Shape::compute(body, &cfg); + } + _ => {} + } + } // TODO self.orig_bytes.to_vec() }