Add early-stage optimization crate (#556)

* Add simple constant folding and folding tests

lib/codegen/src/context.rs

@@ -22,11 +22,11 @@ use licm::do_licm;
 use loop_analysis::LoopAnalysis;
 use nan_canonicalization::do_nan_canonicalization;
 use postopt::do_postopt;
-use preopt::do_preopt;
 use regalloc;
 use result::CodegenResult;
 use settings::{FlagsOrIsa, OptLevel};
 use simple_gvn::do_simple_gvn;
+use simple_preopt::do_preopt;
 use std::vec::Vec;
 use timing;
 use unreachable_code::eliminate_unreachable_code;

lib/codegen/src/lib.rs

@@ -104,12 +104,12 @@ mod nan_canonicalization;
 mod partition_slice;
 mod postopt;
 mod predicates;
-mod preopt;
 mod ref_slice;
 mod regalloc;
 mod result;
 mod scoped_hash_map;
 mod simple_gvn;
+mod simple_preopt;
 mod stack_layout;
 mod topo_order;
 mod unreachable_code;

lib/codegen/src/timing.rs

@@ -124,7 +124,7 @@ mod details {
     }
 
     /// Accumulated timing information for a single pass.
-    #[derive(Default)]
+    #[derive(Default, Copy, Clone)]
     struct PassTime {
         /// Total time spent running this pass including children.
         total: Duration,
@@ -134,17 +134,24 @@ mod details {
     }
 
     /// Accumulated timing for all passes.
-    #[derive(Default)]
     pub struct PassTimes {
         pass: [PassTime; NUM_PASSES],
     }
 
+    impl Default for PassTimes {
+        fn default() -> Self {
+            PassTimes {
+                pass: [Default::default(); NUM_PASSES],
+            }
+        }
+    }
+
     impl fmt::Display for PassTimes {
         fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
             writeln!(f, "======== ========  ==================================")?;
             writeln!(f, "   Total     Self  Pass")?;
             writeln!(f, "-------- --------  ----------------------------------")?;
-            for (time, desc) in self.pass.iter().zip(&DESCRIPTIONS) {
+            for (time, desc) in self.pass.iter().zip(&DESCRIPTIONS[..]) {
                 // Omit passes that haven't run.
                 if time.total == Duration::default() {
                     continue;
@@ -212,7 +219,7 @@ mod details {
     /// Add `timings` to the accumulated timings for the current thread.
     pub fn add_to_current(times: &PassTimes) {
         PASS_TIME.with(|rc| {
-            for (a, b) in rc.borrow_mut().pass.iter_mut().zip(&times.pass) {
+            for (a, b) in rc.borrow_mut().pass.iter_mut().zip(&times.pass[..]) {
                 a.total += b.total;
                 a.child += b.child;
             }