Commit 135580c1621513e7cfeed8098c087d1d6941fa97 | zig

author	Andrew Kelley <andrew@ziglang.org> 2020-07-13 23:48:54-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2020-07-13 23:48:54-07:00
log	135580c1621513e7cfeed8098c087d1d6941fa97
tree	1a27c301ae4f98002cb9a54ff6d28d5f772ca742
parent	5da5ded74326fce0ca52c6cb00f22824f7beb7eb

stage2: fix liveness analysis of Call instructions

2 files changed, 40 insertions(+), 16 deletions(-)

src-self-hosted
- ir.zig
- liveness.zig

src-self-hosted/ir.zig+13-8

 @@ -14,30 +14,35 @@ pub const Inst = struct {
     tag: Tag,
     /// Each bit represents the index of an `Inst` parameter in the `args` field.
     /// If a bit is set, it marks the end of the lifetime of the corresponding
-    /// instruction parameter. For example, 0b000_00101 means that the first and
+    /// instruction parameter. For example, 0b101 means that the first and
     /// third `Inst` parameters' lifetimes end after this instruction, and will
     /// not have any more following references.
     /// The most significant bit being set means that the instruction itself is
     /// never referenced, in other words its lifetime ends as soon as it finishes.
-    /// If bit 7 (0b1xxx_xxxx) is set, it means this instruction itself is unreferenced.
+    /// If bit 15 (0b1xxx_xxxx_xxxx_xxxx) is set, it means this instruction itself is unreferenced.
-    /// If bit 6 (0bx1xx_xxxx) is set, it means this is a special case and the
+    /// If bit 14 (0bx1xx_xxxx_xxxx_xxxx) is set, it means this is a special case and the
     /// lifetimes of operands are encoded elsewhere.
-    deaths: u8 = undefined,
+    deaths: DeathsInt = undefined,
     ty: Type,
     /// Byte offset into the source.
     src: usize,
+    pub const DeathsInt = u16;
+    pub const DeathsBitIndex = std.math.Log2Int(DeathsInt);
+    pub const unreferenced_bit_index = @typeInfo(DeathsInt).Int.bits - 1;
+    pub const deaths_bits = unreferenced_bit_index - 1;
     pub fn isUnused(self: Inst) bool {
-        return (self.deaths & 0b1000_0000) != 0;
+        return (self.deaths & (1 << unreferenced_bit_index)) != 0;
     }
-    pub fn operandDies(self: Inst, index: u3) bool {
+    pub fn operandDies(self: Inst, index: DeathsBitIndex) bool {
-        assert(index < 6);
+        assert(index < deaths_bits);
         return @truncate(u1, self.deaths << index) != 0;
     }
     pub fn specialOperandDeaths(self: Inst) bool {
-        return (self.deaths & 0b1000_0000) != 0;
+        return (self.deaths & (1 << deaths_bits)) != 0;
     }
     pub const Tag = enum {

src-self-hosted/liveness.zig+27-8

 @@ -34,7 +34,7 @@ fn analyzeInstGeneric(arena: *std.mem.Allocator, table: *std.AutoHashMap(*ir.Ins
     inline for (std.meta.declarations(ir.Inst)) |decl| {
         switch (decl.data) {
             .Type => |T| {
-                if (@hasDecl(T, "base_tag")) {
+                if (@typeInfo(T) == .Struct and @hasDecl(T, "base_tag")) {
                     if (T.base_tag == base.tag) {
                         return analyzeInst(arena, table, T, @fieldParentPtr(T, "base", base));
                     }
 @@ -47,7 +47,13 @@ fn analyzeInstGeneric(arena: *std.mem.Allocator, table: *std.AutoHashMap(*ir.Ins
 }
 fn analyzeInst(arena: *std.mem.Allocator, table: *std.AutoHashMap(*ir.Inst, void), comptime T: type, inst: *T) error{OutOfMemory}!void {
-    inst.base.deaths = 0;
+    if (table.contains(&inst.base)) {
+        inst.base.deaths = 0;
+    } else {
+        // No tombstone for this instruction means it is never referenced,
+        // and its birth marks its own death. Very metal 🤘
+        inst.base.deaths = 1 << ir.Inst.unreferenced_bit_index;
+    }
     switch (T) {
         ir.Inst.Constant => return,
 @@ -106,15 +112,28 @@ fn analyzeInst(arena: *std.mem.Allocator, table: *std.AutoHashMap(*ir.Inst, void
             // instruction, and the deaths flag for the CondBr instruction will indicate whether the
             // condition's lifetime ends immediately before entering any branch.
         },
+        ir.Inst.Call => {
+            // Call instructions have a runtime-known number of operands so we have to handle them ourselves here.
+            const needed_bits = 1 + inst.args.args.len;
+            if (needed_bits <= ir.Inst.deaths_bits) {
+                var bit_i: ir.Inst.DeathsBitIndex = 0;
+                {
+                    const prev = try table.fetchPut(inst.args.func, {});
+                    if (prev == null) inst.base.deaths |= @as(ir.Inst.DeathsInt, 1) << bit_i;
+                    bit_i += 1;
+                }
+                for (inst.args.args) |arg| {
+                    const prev = try table.fetchPut(arg, {});
+                    if (prev == null) inst.base.deaths |= @as(ir.Inst.DeathsInt, 1) << bit_i;
+                    bit_i += 1;
+                }
+            } else {
+                @panic("Handle liveness analysis for function calls with many parameters");
+            }
+        },
         else => {},
     }
-    if (!table.contains(&inst.base)) {
-        // No tombstone for this instruction means it is never referenced,
-        // and its birth marks its own death. Very metal 🤘
-        inst.base.deaths |= 1 << 7;
-    }
     const Args = ir.Inst.Args(T);
     if (Args == void) {
         return;