Remove reserved_reg functionality. (#424)

* Remove reserved_reg functionality.

This wasn't implemented, and if we need it in the future, it seems like
it would be better to extend the concept of global values to cover this.

* Use GlobalValue::reserved_value() for sentinal values.

lib/codegen/src/ir/heap.rs

@@ -7,8 +7,8 @@ use std::fmt;
 /// Information about a heap declaration.
 #[derive(Clone)]
 pub struct HeapData {
-    /// Method for determining the heap base address.
-    pub base: HeapBase,
+    /// The address of the start of the heap's storage.
+    pub base: GlobalValue,
 
     /// Guaranteed minimum heap size in bytes. Heap accesses before `min_size` don't need bounds
     /// checking.
@@ -21,18 +21,6 @@ pub struct HeapData {
     pub style: HeapStyle,
 }
 
-/// Method for determining the base address of a heap.
-#[derive(Clone)]
-pub enum HeapBase {
-    /// The heap base lives in a reserved register.
-    ///
-    /// This feature is not yet implemented.
-    ReservedReg,
-
-    /// The heap base is a global value.
-    GlobalValue(GlobalValue),
-}
-
 /// Style of heap including style-specific information.
 #[derive(Clone)]
 pub enum HeapStyle {
@@ -57,12 +45,7 @@ impl fmt::Display for HeapData {
             HeapStyle::Static { .. } => "static",
         })?;
 
-        match self.base {
-            HeapBase::ReservedReg => write!(f, " reserved_reg")?,
-            HeapBase::GlobalValue(gv) => write!(f, " {}", gv)?,
-        }
-
-        write!(f, ", min {}", self.min_size)?;
+        write!(f, " {}, min {}", self.base, self.min_size)?;
         match self.style {
             HeapStyle::Dynamic { bound_gv } => write!(f, ", bound {}", bound_gv)?,
             HeapStyle::Static { bound } => write!(f, ", bound {}", bound)?,

lib/codegen/src/ir/mod.rs

@@ -31,7 +31,7 @@ pub use ir::extfunc::{AbiParam, ArgumentExtension, ArgumentPurpose, ExtFuncData,
 pub use ir::extname::ExternalName;
 pub use ir::function::Function;
 pub use ir::globalvalue::GlobalValueData;
-pub use ir::heap::{HeapBase, HeapData, HeapStyle};
+pub use ir::heap::{HeapData, HeapStyle};
 pub use ir::instructions::{InstructionData, Opcode, ValueList, ValueListPool, VariableArgs};
 pub use ir::jumptable::JumpTableData;
 pub use ir::layout::Layout;

lib/codegen/src/legalizer/heap.rs

@@ -154,11 +154,7 @@ fn offset_addr(
     }
 
     // Add the heap base address base
-    match pos.func.heaps[heap].base {
-        ir::HeapBase::ReservedReg => unimplemented!(),
-        ir::HeapBase::GlobalValue(base_gv) => {
-            let base = pos.ins().global_value(addr_ty, base_gv);
-            pos.func.dfg.replace(inst).iadd(base, offset);
-        }
-    }
+    let base_gv = pos.func.heaps[heap].base;
+    let base = pos.ins().global_value(addr_ty, base_gv);
+    pos.func.dfg.replace(inst).iadd(base, offset);
 }