wasm: simplify merging of branches

Rather than adding all values that were generated in the child branch,
we simply discard them as outer branches cannot refer to values
produced from an inner branch.

1 files changed, 30 insertions, 42 deletions

diff --git a/src/arch/wasm/CodeGen.zig b/src/arch/wasm/CodeGen.zig
index f602cf80a7..04b9b7194c 100644
--- a/src/arch/wasm/CodeGen.zig
+++ b/src/arch/wasm/CodeGen.zig
@@ -3259,9 +3259,13 @@ fn airBlock(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
         .label = func.block_depth,
         .value = block_result,
     });
+
     try func.genBody(body);
     try func.endBlock();
 
+    const liveness = func.liveness.getBlock(inst);
+    try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.deaths.len);
+
     func.finishAir(inst, block_result, &.{});
 }
 
@@ -3316,41 +3320,27 @@ fn airCondBr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     try func.addLabel(.br_if, 0);
 
     try func.branches.ensureUnusedCapacity(func.gpa, 2);
-
-    func.branches.appendAssumeCapacity(.{});
-    try func.currentBranch().values.ensureUnusedCapacity(func.gpa, @intCast(u32, liveness_condbr.else_deaths.len));
-    try func.genBody(else_body);
-    try func.endBlock();
-    var else_stack = func.branches.pop();
-    defer else_stack.deinit(func.gpa);
+    {
+        func.branches.appendAssumeCapacity(.{});
+        try func.currentBranch().values.ensureUnusedCapacity(func.gpa, @intCast(u32, liveness_condbr.else_deaths.len));
+        try func.genBody(else_body);
+        try func.endBlock();
+        var else_stack = func.branches.pop();
+        else_stack.deinit(func.gpa);
+    }
 
     // Outer block that matches the condition
-    func.branches.appendAssumeCapacity(.{});
-    try func.currentBranch().values.ensureUnusedCapacity(func.gpa, @intCast(u32, liveness_condbr.then_deaths.len));
-    try func.genBody(then_body);
-    var then_stack = func.branches.pop();
-    defer then_stack.deinit(func.gpa);
-
-    try func.mergeBranch(&else_stack);
-    try func.mergeBranch(&then_stack);
+    {
+        func.branches.appendAssumeCapacity(.{});
+        try func.currentBranch().values.ensureUnusedCapacity(func.gpa, @intCast(u32, liveness_condbr.then_deaths.len));
+        try func.genBody(then_body);
+        var then_stack = func.branches.pop();
+        then_stack.deinit(func.gpa);
+    }
 
     func.finishAir(inst, .none, &.{});
 }
 
-fn mergeBranch(func: *CodeGen, branch: *const Branch) !void {
-    const parent = func.currentBranch();
-
-    const target_slice = branch.values.entries.slice();
-    const target_keys = target_slice.items(.key);
-    const target_values = target_slice.items(.value);
-
-    try parent.values.ensureTotalCapacity(func.gpa, parent.values.capacity() + branch.values.count());
-    for (target_keys, 0..) |key, index| {
-        // TODO: process deaths from branches
-        parent.values.putAssumeCapacity(key, target_values[index]);
-    }
-}
-
 fn airCmp(func: *CodeGen, inst: Air.Inst.Index, op: std.math.CompareOperator) InnerError!void {
     const bin_op = func.air.instructions.items(.data)[inst].bin_op;
 
@@ -3860,30 +3850,21 @@ fn airSwitchBr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
             }
         }
         func.branches.appendAssumeCapacity(.{});
-
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.deaths[index].len);
-        for (liveness.deaths[index]) |operand| {
-            func.processDeath(Air.indexToRef(operand));
-        }
         try func.genBody(case.body);
         try func.endBlock();
         var case_branch = func.branches.pop();
-        defer case_branch.deinit(func.gpa);
-        try func.mergeBranch(&case_branch);
+        case_branch.deinit(func.gpa);
     }
 
     if (has_else_body) {
         func.branches.appendAssumeCapacity(.{});
         const else_deaths = liveness.deaths.len - 1;
         try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.deaths[else_deaths].len);
-        for (liveness.deaths[else_deaths]) |operand| {
-            func.processDeath(Air.indexToRef(operand));
-        }
         try func.genBody(else_body);
         try func.endBlock();
         var else_branch = func.branches.pop();
-        defer else_branch.deinit(func.gpa);
-        try func.mergeBranch(&else_branch);
+        else_branch.deinit(func.gpa);
     }
     func.finishAir(inst, .none, &.{});
 }
@@ -5992,7 +5973,7 @@ fn airTry(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const extra = func.air.extraData(Air.Try, pl_op.payload);
     const body = func.air.extra[extra.end..][0..extra.data.body_len];
     const err_union_ty = func.air.typeOf(pl_op.operand);
-    const result = try lowerTry(func, err_union, body, err_union_ty, false);
+    const result = try lowerTry(func, inst, err_union, body, err_union_ty, false);
     func.finishAir(inst, result, &.{pl_op.operand});
 }
 
@@ -6002,12 +5983,13 @@ fn airTryPtr(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
     const err_union_ptr = try func.resolveInst(extra.data.ptr);
     const body = func.air.extra[extra.end..][0..extra.data.body_len];
     const err_union_ty = func.air.typeOf(extra.data.ptr).childType();
-    const result = try lowerTry(func, err_union_ptr, body, err_union_ty, true);
+    const result = try lowerTry(func, inst, err_union_ptr, body, err_union_ty, true);
     func.finishAir(inst, result, &.{extra.data.ptr});
 }
 
 fn lowerTry(
     func: *CodeGen,
+    inst: Air.Inst.Index,
     err_union: WValue,
     body: []const Air.Inst.Index,
     err_union_ty: Type,
@@ -6035,8 +6017,14 @@ fn lowerTry(
         }
         try func.addTag(.i32_eqz);
         try func.addLabel(.br_if, 0); // jump out of block when error is '0'
+
+        const liveness = func.liveness.getCondBr(inst);
+        try func.branches.append(func.gpa, .{});
+        try func.currentBranch().values.ensureUnusedCapacity(func.gpa, liveness.else_deaths.len + liveness.then_deaths.len);
         try func.genBody(body);
         try func.endBlock();
+        var branch = func.branches.pop();
+        branch.deinit(func.gpa);
     }
 
     // if we reach here it means error was not set, and we want the payload