Cretonne IL frontend: ILBuilder (#97)

* API and data structures proposal for the SSA construction module

* Polished API and implemented trivial functions

* API more explicit, Variable now struct parameter

* Sample test written to see how the API could be used

* Implemented local value numbering for SSABuilder

* Implemented SSA within a single Ebb

* Unfinished unoptimized implementation for recursive use and seal

* Working global value numbering
The SSABuilder now create ebb args and modifies jump instructions accordingly

* Updated doc and improved branch argument modifying.
Removed instructions::branch_arguments and instructions::branch_argument_mut

* SSA building: bugfix, asserts and new test case
Missing a key optimization to remove cycles of Phi

* SSA Building: small changes after code review
Created helper function for seal_block (which now contains sanity checks)

* Optimization: removed useless phis (ebb arguments)
Using pessimistic assumption that when using a non-def variable in an unsealed block we create an ebb argument which is removed when sealing if we detect it as useless
Using aliases to avoid rewriting variables

* Changed the semantics of remove_ebb_arg and turned it into a proper API method

* Adapted ssa branch to changes in the DFG API

* Abandonned SparseMaps for EntityMaps, added named structure for headr block data.

* Created skeletton for a Cretonne IL builder frontend

* Frontend IL builder: first draft of implementation with example of instruction methods

* Working basic implementation of the frontend
Missing handling of function arguments and return values

* Interaction with function signature, sample test, more checks

* Test with function verifier, seal and fill sanity check

* Implemented python script to generate ILBuilder methods

* Added support for jump tables and stack slot

* Major API overhaul
* No longer generating rust through Python but implements InstBuilder
* No longer parametrized by user's blocks but use regular `Ebb`
* Reuse of allocated memory via distinction between ILBuilder and FunctionBuilder

* Integrate changes from StackSlot

* Improved error message

* Added support for jump arguments supplied by the user

* Added an ebb_args proxy method needed

* Adapted to Entity_ref splitted into a new module

* Better error messages and fixed tests

* Added method to change jump destination

* We whould be able to add unreachable code

* Added inst_result proxy to frontend

* Import support

* Added optimization for SSA construction:
If multiple predecessors but agree on value don't create EBB argument

* Move unsafe and not write-only funcs apart, improved doc

* Added proxy function for append_ebb_arg

* Support for unreachable code and better layout of the Ebbs

* Fixed a bug yielding an infinite loop in SSA construction

* SSA predecessors lookup code refactoring

* Fixed bug in unreachable definition

* New sanity check and display debug function

* Fixed bug in verifier and added is_pristine ;ethod for frontend

* Extended set of characters printable in function names
To be able to print names of functions in test suite

* Fixes and improvements of SSA construction after code review

* Bugfixes for frontend code simplification

* On-the-fly critical edge splitting in case of br_table with jump arguments

* No more dangling undefined values, now attached as EBB args

* Bugfix: only split corresponding edges on demand, not all br_table edges

* Added signature retrieval method

* Bugfix for critical edge splitting not sealing the ebbs it created

* Proper handling of SSA side effects by the frontend

* Code refactoring: moving frontend and SSA to new crate

* Frontend: small changes and bugfixes after code review

lib/cretonne/src/ir/builder.rs

@@ -23,6 +23,8 @@ pub trait InstBuilderBase<'f>: Sized {
     /// Get an immutable reference to the data flow graph that will hold the constructed
     /// instructions.
     fn data_flow_graph(&self) -> &DataFlowGraph;
+    /// Get a mutable reference to the data flow graph that will hold the constructed
+    /// instructions.
     fn data_flow_graph_mut(&mut self) -> &mut DataFlowGraph;
 
     /// Insert an instruction and return a reference to it, consuming the builder.

lib/cretonne/src/ir/dfg.rs

@@ -728,6 +728,37 @@ impl DataFlowGraph {
         num as usize
     }
 
+    /// Removes `val` from `ebb`'s arguments by a standard linear time list removal which preserves
+    /// ordering. Also updates the values' data.
+    pub fn remove_ebb_arg(&mut self, val: Value) {
+        let (ebb, num) = if let ValueData::Arg { num, ebb, .. } = self.values[val] {
+            (ebb, num)
+        } else {
+            panic!("{} must be an EBB argument", val);
+        };
+        self.ebbs[ebb]
+            .args
+            .remove(num as usize, &mut self.value_lists);
+        for index in num..(self.ebb_args(ebb).len() as u16) {
+            match self.values[self.ebbs[ebb]
+                      .args
+                      .get(index as usize, &self.value_lists)
+                      .unwrap()] {
+                ValueData::Arg { ref mut num, .. } => {
+                    *num -= 1;
+                }
+                _ => {
+                    panic!("{} must be an EBB argument",
+                           self.ebbs[ebb]
+                               .args
+                               .get(index as usize, &self.value_lists)
+                               .unwrap())
+                }
+            }
+        }
+    }
+
+
     /// Append an existing argument value to `ebb`.
     ///
     /// The appended value can't already be attached to something else.

lib/cretonne/src/ir/mod.rs

@@ -31,6 +31,7 @@ pub use ir::function::Function;
 pub use ir::builder::InstBuilder;
 pub use ir::progpoint::{ProgramPoint, ProgramOrder, ExpandedProgramPoint};
 pub use ir::memflags::MemFlags;
+pub use ir::builder::InstBuilderBase;
 
 use binemit;
 use entity_map::EntityMap;

lib/cretonne/src/lib.rs

@@ -24,6 +24,7 @@ pub mod flowgraph;
 pub mod ir;
 pub mod isa;
 pub mod loop_analysis;
+pub mod packed_option;
 pub mod regalloc;
 pub mod result;
 pub mod settings;
@@ -36,7 +37,6 @@ mod context;
 mod iterators;
 mod legalizer;
 mod licm;
-mod packed_option;
 mod partition_slice;
 mod predicates;
 mod ref_slice;