Implement jump tables (#453)

* Add 'jump_table_entry' and 'indirect_jump' instructions.

* Update CodeSink to keep track of code size. Pretty up clif-util's disassembly output.

* Only disassemble the machine portion of output. Pretty print the read-only data after it.

* Update switch frontend code to use new br_table instruction w/ default.

lib/codegen/src/ir/function.rs

@@ -11,7 +11,8 @@ use ir::{
     Ebb, ExtFuncData, FuncRef, GlobalValue, GlobalValueData, Heap, HeapData, JumpTable,
     JumpTableData, SigRef, StackSlot, StackSlotData, Table, TableData,
 };
-use ir::{EbbOffsets, InstEncodings, JumpTables, SourceLocs, StackSlots, ValueLocations};
+use ir::{EbbOffsets, InstEncodings, SourceLocs, StackSlots, ValueLocations};
+use ir::{JumpTableOffsets, JumpTables};
 use isa::{EncInfo, Encoding, Legalize, TargetIsa};
 use settings::CallConv;
 use std::fmt;
@@ -64,6 +65,9 @@ pub struct Function {
     /// in the textual IR format.
     pub offsets: EbbOffsets,
 
+    /// Code offsets of Jump Table headers.
+    pub jt_offsets: JumpTableOffsets,
+
     /// Source locations.
     ///
     /// Track the original source location for each instruction. The source locations are not
@@ -87,6 +91,7 @@ impl Function {
             encodings: SecondaryMap::new(),
             locations: SecondaryMap::new(),
             offsets: SecondaryMap::new(),
+            jt_offsets: SecondaryMap::new(),
             srclocs: SecondaryMap::new(),
         }
     }

lib/codegen/src/ir/instructions.rs

@@ -194,7 +194,10 @@ impl InstructionData {
                 ref args,
                 ..
             } => BranchInfo::SingleDest(destination, &args.as_slice(pool)[2..]),
-            InstructionData::BranchTable { table, .. } => BranchInfo::Table(table),
+            InstructionData::BranchTable {
+                table, destination, ..
+            } => BranchInfo::Table(table, Some(destination)),
+            InstructionData::IndirectJump { table, .. } => BranchInfo::Table(table, None),
             _ => {
                 debug_assert!(!self.opcode().is_branch());
                 BranchInfo::NotABranch
@@ -213,7 +216,7 @@ impl InstructionData {
             | InstructionData::BranchInt { destination, .. }
             | InstructionData::BranchFloat { destination, .. }
             | InstructionData::BranchIcmp { destination, .. } => Some(destination),
-            InstructionData::BranchTable { .. } => None,
+            InstructionData::BranchTable { .. } | InstructionData::IndirectJump { .. } => None,
             _ => {
                 debug_assert!(!self.opcode().is_branch());
                 None
@@ -284,8 +287,8 @@ pub enum BranchInfo<'a> {
     /// This is a branch or jump to a single destination EBB, possibly taking value arguments.
     SingleDest(Ebb, &'a [Value]),
 
-    /// This is a jump table branch which can have many destination EBBs.
-    Table(JumpTable),
+    /// This is a jump table branch which can have many destination EBBs and maybe one default EBB.
+    Table(JumpTable, Option<Ebb>),
 }
 
 /// Information about call instructions.

lib/codegen/src/ir/jumptable.rs

@@ -45,6 +45,11 @@ impl JumpTableData {
         self.table.len()
     }
 
+    /// Boolean that is false if the table has missing entries.
+    pub fn fully_dense(&self) -> bool {
+        self.holes == 0
+    }
+
     /// Set a table entry.
     ///
     /// The table will grow as needed to fit `idx`.

lib/codegen/src/ir/mod.rs

@@ -62,5 +62,8 @@ pub type InstEncodings = SecondaryMap<Inst, isa::Encoding>;
 /// Code offsets for EBBs.
 pub type EbbOffsets = SecondaryMap<Ebb, binemit::CodeOffset>;
 
+/// Code offsets for Jump Tables.
+pub type JumpTableOffsets = SecondaryMap<JumpTable, binemit::CodeOffset>;
+
 /// Source locations for instructions.
 pub type SourceLocs = SecondaryMap<Inst, SourceLoc>;