Rename "local variables" to "explicit stack slots".

The term "local variables" predated the SSA builder in the front-end
crate, which also provides a way to implement source-language local
variables. The name "explicit stack slot" makes it clear what this
construct is.

cranelift/docs/example.cton

@@ -1,7 +1,7 @@
 test verifier
 
 function %average(i32, i32) -> f32 native {
-    ss1 = local 8            ; Stack slot for ``sum``.
+    ss1 = explicit_slot 8         ; Stack slot for ``sum``.
 
 ebb1(v1: i32, v2: i32):
     v3 = f64const 0x0.0

cranelift/docs/langref.rst

@@ -37,7 +37,7 @@ The first line of a function definition provides the function *name* and
 the :term:`function signature` which declares the parameter and return types.
 Then follows the :term:`function preamble` which declares a number of entities
 that can be referenced inside the function. In the example above, the preamble
-declares a single local variable, ``ss1``.
+declares a single explicit stack slot, ``ss1``.
 
 After the preamble follows the :term:`function body` which consists of
 :term:`extended basic block`\s (EBBs), the first of which is the
@@ -471,8 +471,8 @@ the expected alignment. By default, misaligned loads and stores are allowed,
 but when the ``aligned`` flag is set, a misaligned memory access is allowed to
 :term:`trap`.
 
-Local variables
----------------
+Explicit Stack Slots
+--------------------
 
 One set of restricted memory operations access the current function's stack
 frame. The stack frame is divided into fixed-size stack slots that are
@@ -480,9 +480,9 @@ allocated in the :term:`function preamble`. Stack slots are not typed, they
 simply represent a contiguous sequence of :term:`accessible` bytes in the stack
 frame.
 
-.. inst:: SS = local Bytes, Flags...
+.. inst:: SS = explicit_slot Bytes, Flags...
 
-    Allocate a stack slot for a local variable in the preamble.
+    Allocate a stack slot in the preamble.
 
     If no alignment is specified, Cretonne will pick an appropriate alignment
     for the stack slot based on its size and access patterns.
@@ -1135,7 +1135,7 @@ Glossary
         A list of declarations of entities that are used by the function body.
         Some of the entities that can be declared in the preamble are:
 
-        - Local variables.
+        - Stack slots.
         - Functions that are called directly.
         - Function signatures for indirect function calls.
         - Function flags and attributes that are not part of the signature.
@@ -1158,9 +1158,16 @@ Glossary
         intermediate representation. Cretonne's IR can be converted to text
         losslessly.
 
-    stack slot
+    explicit stack slot
         A fixed size memory allocation in the current function's activation
-        frame. Also called a local variable.
+        frame. These differ from :term:`spill stack slots` in that they can
+        be created by frontends and they may have their addresses taken.
+
+    spill stack slot
+        A fixed size memory allocation in the current function's activation
+        frame. These differ from :term:`explicit stack slots` in that they are
+        only created during register allocation, and they may not have their
+        address taken.
 
     terminator instruction
         A control flow instruction that unconditionally directs the flow of

cranelift/filetests/isa/intel/prologue-epilogue.cton

@@ -4,13 +4,13 @@ set is_compressed
 isa intel haswell
 
 function %foo() {
-    ss0 = local 168
+    ss0 = explicit_slot 168
 ebb0:
     return
 }
 
 ; check: function %foo(i64 fp [%rbp], i64 csr [%rbx], i64 csr [%r12], i64 csr [%r13], i64 csr [%r14], i64 csr [%r15]) -> i64 fp [%rbp], i64 csr [%rbx], i64 csr [%r12], i64 csr [%r13], i64 csr [%r14], i64 csr [%r15] native {
-; nextln:     ss0 = local 168, offset -224
+; nextln:     ss0 = explicit_slot 168, offset -224
 ; nextln:     ss1 = incoming_arg 56, offset -56
 ; check: ebb0(v0: i64 [%rbp], v1: i64 [%rbx], v2: i64 [%r12], v3: i64 [%r13], v4: i64 [%r14], v5: i64 [%r15]):
 ; nextln:     x86_push v0
@@ -29,4 +29,4 @@ ebb0:
 ; nextln:     v7 = x86_pop.i64
 ; nextln:     v6 = x86_pop.i64
 ; nextln:     return v6, v7, v8, v9, v10, v11
-; nextln: }
+; nextln: }

cranelift/filetests/parser/tiny.cton

@@ -124,7 +124,7 @@ ebb0(v90: i32, v91: f32):
 ; Stack slot references
 function %stack() {
     ss10 = spill_slot 8
-    ss2 = local 4
+    ss2 = explicit_slot 4
     ss3 = incoming_arg 4, offset 8
     ss4 = outgoing_arg 4
     ss5 = emergency_slot 4
@@ -136,7 +136,7 @@ ebb0:
     stack_store v2, ss2
 }
 ; sameln: function %stack() native {
-; check:     ss2 = local 4
+; check:     ss2 = explicit_slot 4
 ; check:     ss3 = incoming_arg 4, offset 8
 ; check:     ss4 = outgoing_arg 4
 ; check:     ss5 = emergency_slot 4

lib/cretonne/src/ir/stackslot.rs

@@ -40,9 +40,9 @@ pub enum StackSlotKind {
     /// A spill slot. This is a stack slot created by the register allocator.
     SpillSlot,
 
-    /// A local variable. This is a chunk of local stack memory for use by the `stack_load` and
-    /// `stack_store` instructions.
-    Local,
+    /// An explicit stack slot. This is a chunk of stack memory for use by the `stack_load`
+    /// and `stack_store` instructions.
+    ExplicitSlot,
 
     /// An incoming function argument.
     ///
@@ -71,7 +71,7 @@ impl FromStr for StackSlotKind {
     fn from_str(s: &str) -> Result<StackSlotKind, ()> {
         use self::StackSlotKind::*;
         match s {
-            "local" => Ok(Local),
+            "explicit_slot" => Ok(ExplicitSlot),
             "spill_slot" => Ok(SpillSlot),
             "incoming_arg" => Ok(IncomingArg),
             "outgoing_arg" => Ok(OutgoingArg),
@@ -85,7 +85,7 @@ impl fmt::Display for StackSlotKind {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use self::StackSlotKind::*;
         f.write_str(match *self {
-            Local => "local",
+            ExplicitSlot => "explicit_slot",
             SpillSlot => "spill_slot",
             IncomingArg => "incoming_arg",
             OutgoingArg => "outgoing_arg",
@@ -366,7 +366,7 @@ mod tests {
         assert_eq!(slot.alignment(8), 8);
         assert_eq!(slot.alignment(16), 8);
 
-        let slot2 = StackSlotData::new(StackSlotKind::Local, 24);
+        let slot2 = StackSlotData::new(StackSlotKind::ExplicitSlot, 24);
 
         assert_eq!(slot2.alignment(4), 4);
         assert_eq!(slot2.alignment(8), 8);

lib/cretonne/src/stack_layout.rs

@@ -7,8 +7,8 @@ use std::cmp::{min, max};
 
 /// Compute the stack frame layout.
 ///
-/// Determine the total size of this stack frame and assign offsets to all `Spill` and `Local`
-/// stack slots.
+/// Determine the total size of this stack frame and assign offsets to all `Spill` and
+/// `Explicit` stack slots.
 ///
 /// The total frame size will be a multiple of `alignment` which must be a power of two.
 ///
@@ -25,7 +25,7 @@ pub fn layout_stack(frame: &mut StackSlots, alignment: StackSize) -> Result<Stac
     // stack layout from high to low addresses will be:
     //
     // 1. incoming arguments.
-    // 2. spills + locals.
+    // 2. spills + explicits.
     // 3. outgoing arguments.
     //
     // The incoming arguments can have both positive and negative offsets. A negative offset
@@ -57,15 +57,15 @@ pub fn layout_stack(frame: &mut StackSlots, alignment: StackSize) -> Result<Stac
                 outgoing_max = max(outgoing_max, offset);
             }
             StackSlotKind::SpillSlot |
-            StackSlotKind::Local |
+            StackSlotKind::ExplicitSlot |
             StackSlotKind::EmergencySlot => {
-                // Determine the smallest alignment of any local or spill slot.
+                // Determine the smallest alignment of any explicit or spill slot.
                 min_align = slot.alignment(min_align);
             }
         }
     }
 
-    // Lay out spill slots and locals below the incoming arguments.
+    // Lay out spill slots and explicit slots below the incoming arguments.
     // The offset is negative, growing downwards.
     // Start with the smallest alignments for better packing.
     let mut offset = incoming_min;
@@ -74,9 +74,10 @@ pub fn layout_stack(frame: &mut StackSlots, alignment: StackSize) -> Result<Stac
         for ss in frame.keys() {
             let slot = frame[ss].clone();
 
-            // Pick out locals and spill slots with exact alignment `min_align`.
+            // Pick out explicit and spill slots with exact alignment `min_align`.
             match slot.kind {
-                StackSlotKind::SpillSlot | StackSlotKind::Local => {
+                StackSlotKind::SpillSlot |
+                StackSlotKind::ExplicitSlot => {
                     if slot.alignment(alignment) != min_align {
                         continue;
                     }

lib/cretonne/src/write.rs

@@ -475,29 +475,29 @@ mod tests {
         f.name = ExternalName::testcase("foo");
         assert_eq!(f.to_string(), "function %foo() native {\n}\n");
 
-        f.create_stack_slot(StackSlotData::new(StackSlotKind::Local, 4));
+        f.create_stack_slot(StackSlotData::new(StackSlotKind::ExplicitSlot, 4));
         assert_eq!(
             f.to_string(),
-            "function %foo() native {\n    ss0 = local 4\n}\n"
+            "function %foo() native {\n    ss0 = explicit_slot 4\n}\n"
         );
 
         let ebb = f.dfg.make_ebb();
         f.layout.append_ebb(ebb);
         assert_eq!(
             f.to_string(),
-            "function %foo() native {\n    ss0 = local 4\n\nebb0:\n}\n"
+            "function %foo() native {\n    ss0 = explicit_slot 4\n\nebb0:\n}\n"
         );
 
         f.dfg.append_ebb_param(ebb, types::I8);
         assert_eq!(
             f.to_string(),
-            "function %foo() native {\n    ss0 = local 4\n\nebb0(v0: i8):\n}\n"
+            "function %foo() native {\n    ss0 = explicit_slot 4\n\nebb0(v0: i8):\n}\n"
         );
 
         f.dfg.append_ebb_param(ebb, types::F32.by(4).unwrap());
         assert_eq!(
             f.to_string(),
-            "function %foo() native {\n    ss0 = local 4\n\nebb0(v0: i8, v1: f32x4):\n}\n"
+            "function %foo() native {\n    ss0 = explicit_slot 4\n\nebb0(v0: i8, v1: f32x4):\n}\n"
         );
     }
 }

lib/reader/src/parser.rs

@@ -1044,7 +1044,7 @@ impl<'a> Parser<'a> {
     // Parse a stack slot decl.
     //
     // stack-slot-decl ::= * StackSlot(ss) "=" stack-slot-kind Bytes {"," stack-slot-flag}
-    // stack-slot-kind ::= "local"
+    // stack-slot-kind ::= "explicit_slot"
     //                   | "spill_slot"
     //                   | "incoming_arg"
     //                   | "outgoing_arg"