From 05b12e677939effa9da147008071908a2a93fe35 Mon Sep 17 00:00:00 2001
From: Jacob Young <jacobly0@users.noreply.github.com>
Date: Tue, 14 Mar 2023 22:32:00 -0400
Subject: [PATCH] x86_64: handle duplicate prong deaths

---
 src/arch/x86_64/CodeGen.zig          | 13 ++++++-------
 test/behavior/inline_switch.zig      |  1 -
 test/behavior/union.zig              |  2 --
 test/behavior/union_with_members.zig |  1 -
 4 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 1be93accc7..bf1d9f0eb0 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -1037,9 +1037,9 @@ fn genBody(self: *Self, body: []const Air.Inst.Index) InnerError!void {
 fn processDeath(self: *Self, inst: Air.Inst.Index) void {
     const air_tags = self.air.instructions.items(.tag);
     if (air_tags[inst] == .constant) return; // Constants are immortal.
+    const prev_value = self.getResolvedInstValue(inst) orelse return;
     log.debug("%{d} => {}", .{ inst, MCValue.dead });
     // When editing this function, note that the logic must synchronize with `reuseOperand`.
-    const prev_value = self.getResolvedInstValue(inst);
     const branch = &self.branch_stack.items[self.branch_stack.items.len - 1];
     branch.inst_table.putAssumeCapacity(inst, .dead);
     switch (prev_value) {
@@ -1225,7 +1225,7 @@ fn revertState(self: *Self, state: State) void {
 pub fn spillInstruction(self: *Self, reg: Register, inst: Air.Inst.Index) !void {
     const stack_mcv = try self.allocRegOrMem(inst, false);
     log.debug("spilling %{d} to stack mcv {any}", .{ inst, stack_mcv });
-    const reg_mcv = self.getResolvedInstValue(inst);
+    const reg_mcv = self.getResolvedInstValue(inst).?;
     switch (reg_mcv) {
         .register => |other| {
             assert(reg.to64() == other.to64());
@@ -1242,7 +1242,7 @@ pub fn spillInstruction(self: *Self, reg: Register, inst: Air.Inst.Index) !void
 
 pub fn spillEflagsIfOccupied(self: *Self) !void {
     if (self.eflags_inst) |inst_to_save| {
-        const mcv = self.getResolvedInstValue(inst_to_save);
+        const mcv = self.getResolvedInstValue(inst_to_save).?;
         const new_mcv = switch (mcv) {
             .register_overflow => try self.allocRegOrMem(inst_to_save, false),
             .eflags => try self.allocRegOrMem(inst_to_save, true),
@@ -6315,18 +6315,17 @@ fn resolveInst(self: *Self, inst: Air.Inst.Ref) InnerError!MCValue {
             return gop.value_ptr.*;
         },
         .const_ty => unreachable,
-        else => return self.getResolvedInstValue(inst_index),
+        else => return self.getResolvedInstValue(inst_index).?,
     }
 }
 
-fn getResolvedInstValue(self: *Self, inst: Air.Inst.Index) MCValue {
+fn getResolvedInstValue(self: *Self, inst: Air.Inst.Index) ?MCValue {
     // Treat each stack item as a "layer" on top of the previous one.
     var i: usize = self.branch_stack.items.len;
     while (true) {
         i -= 1;
         if (self.branch_stack.items[i].inst_table.get(inst)) |mcv| {
-            assert(mcv != .dead);
-            return mcv;
+            return if (mcv != .dead) mcv else null;
         }
     }
 }
diff --git a/test/behavior/inline_switch.zig b/test/behavior/inline_switch.zig
index 90e8b36284..dcd603c94f 100644
--- a/test/behavior/inline_switch.zig
+++ b/test/behavior/inline_switch.zig
@@ -46,7 +46,6 @@ const U = union(E) { a: void, b: u2, c: u3, d: u4 };
 test "inline switch unions" {
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
 
     var x: U = .a;
diff --git a/test/behavior/union.zig b/test/behavior/union.zig
index 03c47b09d6..9b49f8bf47 100644
--- a/test/behavior/union.zig
+++ b/test/behavior/union.zig
@@ -214,7 +214,6 @@ const Payload = union(Letter) {
 };
 
 test "union with specified enum tag" {
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
@@ -224,7 +223,6 @@ test "union with specified enum tag" {
 }
 
 test "packed union generates correctly aligned type" {
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
diff --git a/test/behavior/union_with_members.zig b/test/behavior/union_with_members.zig
index 0cb06a81ab..8e9c2db475 100644
--- a/test/behavior/union_with_members.zig
+++ b/test/behavior/union_with_members.zig
@@ -18,7 +18,6 @@ const ET = union(enum) {
 
 test "enum with members" {
     if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO