Rename the 'cretonne' crate to 'cretonne-codegen'.

This fixes the next part of #287.

lib/codegen/src/simple_gvn.rs

@@ -0,0 +1,84 @@
+//! A simple GVN pass.
+
+use cursor::{Cursor, FuncCursor};
+use dominator_tree::DominatorTree;
+use ir::{Function, Inst, InstructionData, Opcode, Type};
+use scoped_hash_map::ScopedHashMap;
+use std::vec::Vec;
+use timing;
+
+/// Test whether the given opcode is unsafe to even consider for GVN.
+fn trivially_unsafe_for_gvn(opcode: Opcode) -> bool {
+    opcode.is_call() || opcode.is_branch() || opcode.is_terminator() ||
+        opcode.is_return() || opcode.can_trap() || opcode.other_side_effects() ||
+        opcode.can_store() || opcode.can_load() || opcode.writes_cpu_flags()
+}
+
+/// Perform simple GVN on `func`.
+///
+pub fn do_simple_gvn(func: &mut Function, domtree: &mut DominatorTree) {
+    let _tt = timing::gvn();
+    debug_assert!(domtree.is_valid());
+
+    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 = FuncCursor::new(func);
+
+    for &ebb in domtree.cfg_postorder().iter().rev() {
+        // Pop any scopes that we just exited.
+        loop {
+            if let Some(current) = scope_stack.last() {
+                if domtree.dominates(*current, ebb, &pos.func.layout) {
+                    break;
+                }
+            } else {
+                break;
+            }
+            scope_stack.pop();
+            visible_values.decrement_depth();
+        }
+
+        // Push a scope for the current block.
+        scope_stack.push(pos.func.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.
+            pos.func.dfg.resolve_aliases_in_arguments(inst);
+
+            let opcode = pos.func.dfg[inst].opcode();
+            if opcode.is_branch() && !opcode.is_terminator() {
+                scope_stack.push(pos.func.layout.next_inst(inst).unwrap());
+                visible_values.increment_depth();
+            }
+            if trivially_unsafe_for_gvn(opcode) {
+                continue;
+            }
+
+            let ctrl_typevar = pos.func.dfg.ctrl_typevar(inst);
+            let key = (pos.func.dfg[inst].clone(), ctrl_typevar);
+            let entry = visible_values.entry(key);
+            use scoped_hash_map::Entry::*;
+            match entry {
+                Occupied(entry) => {
+                    debug_assert!(domtree.dominates(*entry.get(), inst, &pos.func.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.func.layout.next_inst(inst).unwrap();
+                    }
+                    // Replace the redundant instruction and remove it.
+                    pos.func.dfg.replace_with_aliases(inst, *entry.get());
+                    pos.remove_inst_and_step_back();
+                }
+                Vacant(entry) => {
+                    entry.insert(inst);
+                }
+            }
+        }
+    }
+}