use saved rregisters when needed

& store and restore saved registers on the stack

1 files changed, 11 insertions, 3 deletions

diff --git a/src/compile.zig b/src/compile.zig
index 0ce170c..3ee3eb0 100644
--- a/src/compile.zig
+++ b/src/compile.zig
@@ -94,6 +94,7 @@ pub const BasicBlock = struct {
     instrs: std.ArrayListUnmanaged(Instr) = .empty,
 
     vreg_last_use: std.AutoHashMapUnmanaged(VReg, usize) = .empty,
+    vreg_used_during_call: std.AutoHashMapUnmanaged(VReg, void) = .empty,
 
     fn finalize(self: *BasicBlock, allocator: Allocator) !void {
         std.debug.assert(self.instrs.items.len > 0);
@@ -102,11 +103,18 @@ pub const BasicBlock = struct {
         });
 
         self.vreg_last_use = .empty;
+        var set_at: std.AutoHashMapUnmanaged(VReg, usize) = .empty;
+        var last_call: usize = 0;
         for (0.., self.instrs.items) |i, instr| {
-            for (instr.sources().slice()) |src|
-                try self.vreg_last_use.put(allocator, src, i);
-            if (instr.dest()) |dest|
+            if (instr.dest()) |dest| {
                 try self.vreg_last_use.put(allocator, dest, i);
+                try set_at.put(allocator, dest, i);
+            }
+            for (instr.sources().slice()) |src| {
+                try self.vreg_last_use.put(allocator, src, i);
+                if (set_at.get(src).? < last_call) try self.vreg_used_during_call.put(allocator, src, {});
+            }
+            if (instr.type == .call) last_call = i;
         }
     }