llvm: handle pointers in packed structs in more places

Closes #12776

src/codegen/llvm.zig

@@ -9204,6 +9204,12 @@ pub const FuncGen = struct {
             return self.builder.buildBitCast(truncated_int, elem_llvm_ty, "");
         }
 
+        if (info.pointee_type.isPtrAtRuntime()) {
+            const same_size_int = self.context.intType(elem_bits);
+            const truncated_int = self.builder.buildTrunc(shifted_value, same_size_int, "");
+            return self.builder.buildIntToPtr(truncated_int, elem_llvm_ty, "");
+        }
+
         return self.builder.buildTrunc(shifted_value, elem_llvm_ty, "");
     }
 
@@ -9235,7 +9241,10 @@ pub const FuncGen = struct {
             // Convert to equally-sized integer type in order to perform the bit
             // operations on the value to store
             const value_bits_type = self.context.intType(elem_bits);
-            const value_bits = self.builder.buildBitCast(elem, value_bits_type, "");
+            const value_bits = if (elem_ty.isPtrAtRuntime())
+                self.builder.buildPtrToInt(elem, value_bits_type, "")
+            else
+                self.builder.buildBitCast(elem, value_bits_type, "");
 
             var mask_val = value_bits_type.constAllOnes();
             mask_val = mask_val.constZExt(containing_int_ty);

test/behavior.zig

@@ -86,6 +86,7 @@ test {
     _ = @import("behavior/bugs/12430.zig");
     _ = @import("behavior/bugs/12486.zig");
     _ = @import("behavior/bugs/12680.zig");
+    _ = @import("behavior/bugs/12776.zig");
     _ = @import("behavior/byteswap.zig");
     _ = @import("behavior/byval_arg_var.zig");
     _ = @import("behavior/call.zig");

test/behavior/bugs/12776.zig

@@ -0,0 +1,42 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+const RAM = struct {
+    data: [0xFFFF + 1]u8,
+    fn new() !RAM {
+        return RAM{ .data = [_]u8{0} ** 0x10000 };
+    }
+    fn get(self: *RAM, addr: u16) u8 {
+        return self.data[addr];
+    }
+};
+
+const CPU = packed struct {
+    interrupts: bool,
+    ram: *RAM,
+    fn new(ram: *RAM) !CPU {
+        return CPU{
+            .ram = ram,
+            .interrupts = false,
+        };
+    }
+    fn tick(self: *CPU) !void {
+        var queued_interrupts = self.ram.get(0xFFFF) & self.ram.get(0xFF0F);
+        if (self.interrupts and queued_interrupts != 0) {
+            self.interrupts = false;
+        }
+    }
+};
+
+test {
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
+
+    var ram = try RAM.new();
+    var cpu = try CPU.new(&ram);
+    try cpu.tick();
+    try std.testing.expect(cpu.interrupts == false);
+}