Sema: use correct value when `@ptrCast` operand is comptime known

Closes #13034

2 files changed, 12 insertions, 1 deletions

diff --git a/src/Sema.zig b/src/Sema.zig
index 109b6f2a22..eb228c824e 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -18352,7 +18352,7 @@ fn zirPtrCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air
         return sema.failWithOwnedErrorMsg(msg);
     }
 
-    if (try sema.resolveMaybeUndefVal(block, operand_src, operand)) |operand_val| {
+    if (try sema.resolveMaybeUndefVal(block, operand_src, ptr)) |operand_val| {
         if (!dest_ty.ptrAllowsZero() and operand_val.isUndef()) {
             return sema.failWithUseOfUndef(block, operand_src);
         }
diff --git a/test/behavior/pointers.zig b/test/behavior/pointers.zig
index 91d398e84d..b0fb0f3a42 100644
--- a/test/behavior/pointers.zig
+++ b/test/behavior/pointers.zig
@@ -483,3 +483,14 @@ test "pointer to constant decl preserves alignment" {
     const alignment = @typeInfo(@TypeOf(&S.aligned)).Pointer.alignment;
     try std.testing.expect(alignment == 8);
 }
+
+test "ptrCast comptime known slice to C pointer" {
+    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_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+
+    const s: [:0]const u8 = "foo";
+    var p = @ptrCast([*c]const u8, s);
+    try std.testing.expectEqualStrings(s, std.mem.sliceTo(p, 0));
+}