Assign stack slots to incoming function arguments.

Function arguments that don't fit in registers are passed on the stack.

Create "incoming_arg" stack slots representing the stack arguments, and
assign them to the value arguments during spilling.

filetests/regalloc/spill.cton

@@ -109,3 +109,15 @@ ebb0(v0: i32):
     ; check: call_indirect $sig0, $v0($v0, $c)
     return
 }
+
+; Two arguments on the stack.
+function %stackargs(i32, i32, i32, i32, i32, i32, i32, i32) -> i32 {
+; check: ss0 = incoming_arg 4
+; check: ss1 = incoming_arg 4, offset 4
+; not: incoming_arg
+ebb0(v0: i32, v1: i32, v2: i32, v3: i32, v4: i32, v5: i32, v6: i32, v7: i32):
+    ; unordered: fill $v6
+    ; unordered: fill $v7
+    v10 = iadd v6, v7
+    return v10
+}

lib/cretonne/src/ir/stackslot.rs

@@ -155,10 +155,10 @@ impl StackSlots {
     }
 
     /// Create a stack slot representing an incoming function argument.
-    pub fn make_incoming_arg(&mut self, ty: Type, offset: u32) -> StackSlot {
+    pub fn make_incoming_arg(&mut self, ty: Type, offset: i32) -> StackSlot {
         let mut data = StackSlotData::new(StackSlotKind::IncomingArg, ty.bytes());
-        assert!(offset <= i32::max_value() as u32 - data.size);
-        data.offset = offset as i32;
+        assert!(offset <= i32::max_value() - data.size as i32);
+        data.offset = offset;
         self.push(data)
     }
 }

lib/cretonne/src/ir/valueloc.rs

@@ -112,6 +112,14 @@ impl ArgumentLoc {
         }
     }
 
+    /// Is this a stack location?
+    pub fn is_stack(&self) -> bool {
+        match *self {
+            ArgumentLoc::Stack(_) => true,
+            _ => false,
+        }
+    }
+
     /// Return an object that can display this argument location, using the register info from the
     /// target ISA.
     pub fn display<'a, R: Into<Option<&'a RegInfo>>>(self, regs: R) -> DisplayArgumentLoc<'a> {

lib/cretonne/src/regalloc/coloring.rs

@@ -253,19 +253,8 @@ impl<'a> Context<'a> {
                     }
 
                 }
-                Affinity::Stack => {
-                    if let ArgumentLoc::Stack(_offset) = abi.location {
-                        // TODO: Allocate a stack slot at incoming offset and assign it.
-                        panic!("Unimplemented {}: {} stack allocation",
-                               lv.value,
-                               abi.display(&self.reginfo));
-                    } else {
-                        // This should have been fixed by the reload pass.
-                        panic!("Entry arg {} has stack affinity, but ABI {}",
-                               lv.value,
-                               abi.display(&self.reginfo));
-                    }
-                }
+                // The spiller will have assigned an incoming stack slot already.
+                Affinity::Stack => assert!(abi.location.is_stack()),
                 // This is a ghost value, unused in the function. Don't assign it to a location
                 // either.
                 Affinity::None => {}

lib/cretonne/src/regalloc/spilling.rs

@@ -17,7 +17,7 @@
 
 use dominator_tree::DominatorTree;
 use ir::{DataFlowGraph, Layout, Cursor, InstBuilder};
-use ir::{Function, Ebb, Inst, Value, ValueLoc, SigRef};
+use ir::{Function, Ebb, Inst, Value, ValueLoc, ArgumentLoc, Signature, SigRef};
 use ir::{InstEncodings, StackSlots, ValueLocations};
 use isa::registers::{RegClass, RegClassMask};
 use isa::{TargetIsa, RegInfo, EncInfo, RecipeConstraints, ConstraintKind};
@@ -45,6 +45,7 @@ struct Context<'a> {
     encodings: &'a mut InstEncodings,
     stack_slots: &'a mut StackSlots,
     locations: &'a mut ValueLocations,
+    func_signature: &'a Signature,
 
     // References to contextual data structures we need.
     domtree: &'a DominatorTree,
@@ -92,6 +93,7 @@ impl Spilling {
             encodings: &mut func.encodings,
             stack_slots: &mut func.stack_slots,
             locations: &mut func.locations,
+            func_signature: &func.signature,
             domtree,
             liveness,
             virtregs,
@@ -109,12 +111,37 @@ impl<'a> Context<'a> {
            layout: &mut Layout,
            dfg: &mut DataFlowGraph,
            tracker: &mut LiveValueTracker) {
+        if let Some(entry) = layout.entry_block() {
+            self.spill_entry_arguments(entry, dfg);
+        }
+
         self.topo.reset(layout.ebbs());
         while let Some(ebb) = self.topo.next(layout, self.domtree) {
             self.visit_ebb(ebb, layout, dfg, tracker);
         }
     }
 
+    /// Assign stack slots to incoming function arguments on the stack.
+    fn spill_entry_arguments(&mut self, entry: Ebb, dfg: &DataFlowGraph) {
+        for (abi, &arg) in self.func_signature
+                .argument_types
+                .iter()
+                .zip(dfg.ebb_args(entry)) {
+            if let ArgumentLoc::Stack(offset) = abi.location {
+                // Function arguments passed on the stack can't be part of a virtual register. We
+                // would need to write other values to the stack slot, but it belongs to the
+                // caller. (Not that the caller would care, nobody depends on stack arguments being
+                // preserved across calls).
+                assert_eq!(self.virtregs.get(arg),
+                           None,
+                           "Stack argument {} can't be part of a virtual register",
+                           arg);
+                let ss = self.stack_slots.make_incoming_arg(abi.value_type, offset);
+                *self.locations.ensure(arg) = ValueLoc::Stack(ss);
+            }
+        }
+    }
+
     fn visit_ebb(&mut self,
                  ebb: Ebb,
                  layout: &mut Layout,