0c7316ae28
* Replace a single-character string literal with a character literal. * Use is_some() instead of comparing with Some(_). * Add code-quotes around type names in comments. * Use !...is_empty() instead of len() != 0. * Tidy up redundant returns. * Remove redundant .clone() calls. * Remove unnecessary explicit lifetime parameters. * Tidy up unnecessary '&'s. * Add parens to make operator precedence explicit. * Use debug_assert_eq instead of debug_assert with ==. * Replace a &Vec argument with a &[...]. * Replace `a = a op b` with `a op= b`. * Avoid unnecessary closures. * Avoid .iter() and .iter_mut() for iterating over containers. * Remove unneeded qualification.
68 lines
2.2 KiB
Rust
68 lines
2.2 KiB
Rust
//! A simple GVN pass.
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use flowgraph::ControlFlowGraph;
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use dominator_tree::DominatorTree;
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use ir::{Cursor, InstructionData, Function, Inst, Opcode};
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use std::collections::HashMap;
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/// Test whether the given opcode is unsafe to even consider for GVN.
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fn trivially_unsafe_for_gvn(opcode: Opcode) -> bool {
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opcode.is_call() || opcode.is_branch() || opcode.is_terminator() || opcode.is_return() ||
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opcode.can_trap()
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}
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/// Perform simple GVN on `func`.
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///
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pub fn do_simple_gvn(func: &mut Function, cfg: &mut ControlFlowGraph) {
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let mut visible_values: HashMap<InstructionData, Inst> = HashMap::new();
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let domtree = DominatorTree::with_function(func, cfg);
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// Visit EBBs in a reverse post-order.
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let mut pos = Cursor::new(&mut func.layout);
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for &ebb in domtree.cfg_postorder().iter().rev() {
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pos.goto_top(ebb);
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while let Some(inst) = pos.next_inst() {
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let opcode = func.dfg[inst].opcode();
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// Resolve aliases, particularly aliases we created earlier.
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func.dfg.resolve_aliases_in_arguments(inst);
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if trivially_unsafe_for_gvn(opcode) {
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continue;
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}
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// TODO: Implement simple redundant-load elimination.
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if opcode.can_store() {
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continue;
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}
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if opcode.can_load() {
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continue;
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}
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let key = func.dfg[inst].clone();
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let entry = visible_values.entry(key);
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use std::collections::hash_map::Entry::*;
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match entry {
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Occupied(mut entry) => {
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if domtree.dominates(*entry.get(), inst, pos.layout) {
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func.dfg.replace_with_aliases(inst, *entry.get());
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pos.remove_inst_and_step_back();
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} else {
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// The prior instruction doesn't dominate inst, so it
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// won't dominate any subsequent instructions we'll
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// visit, so just replace it.
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*entry.get_mut() = inst;
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continue;
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}
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}
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Vacant(entry) => {
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entry.insert(inst);
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}
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}
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}
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}
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}
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