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Use ScopedHashMap in simple_gvn.

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This avoids effectively ending up with most of a function body
stored in the hash map at once by removing elements promptly when
they go out of scope.
This commit is contained in:
Dan Gohman
2017-09-19 21:05:53 -07:00
parent 6710216e96
commit ce94a3fa39
2 changed files with 111 additions and 14 deletions
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76
cranelift/filetests/simple_gvn/scopes.cton Normal file
View File

@@ -0,0 +1,76 @@
test simple-gvn
function %two_diamonds(i32, i32, i32, i32, i32) {
ebb0(v0: i32, v1: i32, v2: i32, v3: i32, v4: i32):
v5 = iconst.i32 16
; check: v5 = iconst.i32 16
brz v0, ebb1
v6 = iconst.i32 17
; check: v6 = iconst.i32 17
v7 = iconst.i32 16
; not: v7 = iconst.i32 16
jump ebb2
ebb1:
v8 = iconst.i32 18
; check: v8 = iconst.i32 18
v9 = iconst.i32 17
; check: v9 = iconst.i32 17
v10 = iconst.i32 16
; not: v10 = iconst.i32 16
jump ebb2
ebb2:
v11 = iconst.i32 19
; check: v11 = iconst.i32 19
v12 = iconst.i32 18
; check: v12 = iconst.i32 18
v13 = iconst.i32 17
; check: v13 = iconst.i32 17
v14 = iconst.i32 16
; not: v14 = iconst.i32 16
brz v1, ebb3
v15 = iconst.i32 20
; check: v15 = iconst.i32 20
v16 = iconst.i32 19
; not: v16 = iconst.i32 19
v17 = iconst.i32 18
; not: v17 = iconst.i32 18
v18 = iconst.i32 17
; not: v18 = iconst.i32 17
v19 = iconst.i32 16
; not: v19 = iconst.i32 16
jump ebb4
ebb3:
v20 = iconst.i32 21
; check: v20 = iconst.i32 21
v21 = iconst.i32 20
; check: v21 = iconst.i32 20
v22 = iconst.i32 19
; not: v22 = iconst.i32 19
v23 = iconst.i32 18
; not: v23 = iconst.i32 18
v24 = iconst.i32 17
; not: v24 = iconst.i32 17
v25 = iconst.i32 16
; not: v25 = iconst.i32 16
jump ebb4
ebb4:
v26 = iconst.i32 22
; check: v26 = iconst.i32 22
v27 = iconst.i32 21
; check: v27 = iconst.i32 21
v28 = iconst.i32 20
; check: v28 = iconst.i32 20
v29 = iconst.i32 19
; not: v29 = iconst.i32 19
v30 = iconst.i32 18
; not: v30 = iconst.i32 18
v31 = iconst.i32 17
; not: v31 = iconst.i32 17
v32 = iconst.i32 16
; not: v32 = iconst.i32 16
return
}

49
lib/cretonne/src/simple_gvn.rs
View File

@@ -3,7 +3,7 @@
use flowgraph::ControlFlowGraph;
use dominator_tree::DominatorTree;
use ir::{Cursor, CursorBase, InstructionData, Function, Inst, Opcode, Type};
use std::collections::HashMap;
use scoped_hash_map::ScopedHashMap;
/// Test whether the given opcode is unsafe to even consider for GVN.
fn trivially_unsafe_for_gvn(opcode: Opcode) -> bool {
@@ -18,19 +18,40 @@ pub fn do_simple_gvn(func: &mut Function, cfg: &mut ControlFlowGraph, domtree: &
debug_assert!(cfg.is_valid());
debug_assert!(domtree.is_valid());
let mut visible_values: HashMap<(InstructionData, Type), Inst> = HashMap::new();
let mut visible_values: ScopedHashMap<(InstructionData, Type), Inst> = ScopedHashMap::new();
let mut scope_stack: Vec<Inst> = Vec::new();
// Visit EBBs in a reverse post-order.
let mut pos = Cursor::new(&mut func.layout);
for &ebb in domtree.cfg_postorder().iter().rev() {
pos.goto_top(ebb);
// Pop any scopes that we just exited.
loop {
if let Some(current) = scope_stack.last() {
if domtree.dominates(*current, ebb, &pos.layout) {
break;
}
} else {
break;
}
scope_stack.pop();
visible_values.decrement_depth();
}
// Push a scope for the current block.
scope_stack.push(pos.layout.first_inst(ebb).unwrap());
visible_values.increment_depth();
pos.goto_top(ebb);
while let Some(inst) = pos.next_inst() {
// Resolve aliases, particularly aliases we created earlier.
func.dfg.resolve_aliases_in_arguments(inst);
let opcode = func.dfg[inst].opcode();
if opcode.is_branch() && !opcode.is_terminator() {
scope_stack.push(pos.layout.next_inst(inst).unwrap());
visible_values.increment_depth();
}
if trivially_unsafe_for_gvn(opcode) {
continue;
}
@@ -38,19 +59,19 @@ pub fn do_simple_gvn(func: &mut Function, cfg: &mut ControlFlowGraph, domtree: &
let ctrl_typevar = func.dfg.ctrl_typevar(inst);
let key = (func.dfg[inst].clone(), ctrl_typevar);
let entry = visible_values.entry(key);
use std::collections::hash_map::Entry::*;
use scoped_hash_map::Entry::*;
match entry {
Occupied(mut entry) => {
if domtree.dominates(*entry.get(), inst, pos.layout) {
func.dfg.replace_with_aliases(inst, *entry.get());
pos.remove_inst_and_step_back();
} else {
// The prior instruction doesn't dominate inst, so it
// won't dominate any subsequent instructions we'll
// visit, so just replace it.
*entry.get_mut() = inst;
continue;
Occupied(entry) => {
debug_assert!(domtree.dominates(*entry.get(), inst, pos.layout));
// If the redundant instruction is representing the current
// scope, pick a new representative.
let old = scope_stack.last_mut().unwrap();
if *old == inst {
*old = pos.layout.next_inst(inst).unwrap();
}
// Replace the redundant instruction and remove it.
func.dfg.replace_with_aliases(inst, *entry.get());
pos.remove_inst_and_step_back();
}
Vacant(entry) => {
entry.insert(inst);