Do not ICE on indirect fn pointers

Fixes #452.

Author: LegNeato

crates/rustc_codegen_spirv/src/linker/simple_passes.rs

@@ -237,10 +237,18 @@ pub fn check_fragment_insts(sess: &Session, module: &Module) -> super::Result<()
         let mut any_err = None;
         for inst in module.functions[index].all_inst_iter() {
             if inst.class.opcode == Op::FunctionCall {
-                let callee = func_id_to_idx[&inst.operands[0].unwrap_id_ref()];
-                let callee_had_err =
-                    visit(sess, module, visited, stack, names, callee, func_id_to_idx).err();
-                any_err = any_err.or(callee_had_err);
+                let callee_id = inst.operands[0].unwrap_id_ref();
+                if let Some(&callee) = func_id_to_idx.get(&callee_id) {
+                    if let Err(e) =
+                        visit(sess, module, visited, stack, names, callee, func_id_to_idx)
+                    {
+                        any_err = any_err.or(Some(e));
+                    }
+                } else {
+                    // Indirect or external callee: nothing to traverse.
+                    // Keep scanning this function for forbidden fragment ops.
+                    continue;
+                }
             }
             if matches!(
                 inst.class.opcode,

tests/compiletests/ui/lang/issue-452.rs

@@ -0,0 +1,40 @@
+// build-fail
+#![feature(stmt_expr_attributes)]
+
+use spirv_std::spirv;
+
+#[derive(Clone, Copy)]
+struct PositionR {
+    position: u32,
+    r: u32,
+}
+
+const ELEMENTS_PER_THREAD: usize = 2;
+
+fn sort_local_bucket(
+    lane_id: u32,
+    local_bucket: &mut [PositionR; ELEMENTS_PER_THREAD],
+    cmp_key: fn(&PositionR) -> u32,
+) {
+    let select_smaller = (lane_id as usize & 1) == 0;
+    let a = local_bucket[0];
+    let b = local_bucket[1];
+
+    let _ = if (cmp_key(&a) <= cmp_key(&b)) == select_smaller {
+        a
+    } else {
+        b
+    };
+}
+
+#[spirv(compute(threads(1)))]
+pub fn main() {
+    let mut bucket = [PositionR { position: 0, r: 0 }; ELEMENTS_PER_THREAD];
+
+    sort_local_bucket(
+        0,
+        &mut bucket,
+        #[inline(always)]
+        |position_r| position_r.position,
+    );
+}

tests/compiletests/ui/lang/issue-452.stderr

@@ -0,0 +1,61 @@
+error: function pointer types are not allowed
+  --> $DIR/issue-452.rs:14:1
+   |
+LL | / fn sort_local_bucket(
+LL | |     lane_id: u32,
+LL | |     local_bucket: &mut [PositionR; ELEMENTS_PER_THREAD],
+LL | |     cmp_key: fn(&PositionR) -> u32,
+LL | | ) {
+   | |_^
+   |
+   = note: used by unnamed global (%14)
+note: used from within `issue_452::sort_local_bucket`
+  --> $DIR/issue-452.rs:14:4
+   |
+LL | fn sort_local_bucket(
+   |    ^^^^^^^^^^^^^^^^^
+note: called by `issue_452::main`
+  --> $DIR/issue-452.rs:34:5
+   |
+LL | /     sort_local_bucket(
+LL | |         0,
+LL | |         &mut bucket,
+LL | |         #[inline(always)]
+LL | |         |position_r| position_r.position,
+LL | |     );
+   | |_____^
+note: called by `main`
+  --> $DIR/issue-452.rs:31:8
+   |
+LL | pub fn main() {
+   |        ^^^^
+
+error: indirect calls are not supported in SPIR-V
+  --> $DIR/issue-452.rs:23:32
+   |
+LL |     let _ = if (cmp_key(&a) <= cmp_key(&b)) == select_smaller {
+   |                                ^^^^^^^^^^^
+   |
+note: used from within `issue_452::sort_local_bucket`
+  --> $DIR/issue-452.rs:14:4
+   |
+LL | fn sort_local_bucket(
+   |    ^^^^^^^^^^^^^^^^^
+note: called by `issue_452::main`
+  --> $DIR/issue-452.rs:34:5
+   |
+LL | /     sort_local_bucket(
+LL | |         0,
+LL | |         &mut bucket,
+LL | |         #[inline(always)]
+LL | |         |position_r| position_r.position,
+LL | |     );
+   | |_____^
+note: called by `main`
+  --> $DIR/issue-452.rs:31:8
+   |
+LL | pub fn main() {
+   |        ^^^^
+
+error: aborting due to 2 previous errors
+