Get closer to testing NO_DCE in CI (#321)

* Get closer to testing NO_DCE in CI

The only remaining validation issues are due to the SROA pass not being
implemented yet

* Revert mistakenly included change

crates/rustc_codegen_spirv/src/abi.rs

@@ -4,7 +4,7 @@
 use crate::codegen_cx::CodegenCx;
 use crate::spirv_type::SpirvType;
 use crate::symbols::{parse_attrs, SpirvAttribute};
-use rspirv::spirv::{StorageClass, Word};
+use rspirv::spirv::{Capability, StorageClass, Word};
 use rustc_middle::bug;
 use rustc_middle::ty::layout::{FnAbiExt, TyAndLayout};
 use rustc_middle::ty::{GeneratorSubsts, PolyFnSig, Ty, TyKind, TypeAndMut};
@@ -33,6 +33,7 @@ impl<'tcx> RecursivePointeeCache<'tcx> {
     fn begin(
         &self,
         cx: &CodegenCx<'tcx>,
+        span: Span,
         pointee: PointeeTy<'tcx>,
         storage_class: StorageClass,
     ) -> Option<Word> {
@@ -52,6 +53,18 @@ impl<'tcx> RecursivePointeeCache<'tcx> {
                     let new_id = cx.emit_global().id();
                     cx.emit_global().type_forward_pointer(new_id, storage_class);
                     entry.insert(PointeeDefState::DefiningWithForward(new_id));
+                    if !cx.builder.has_capability(Capability::Addresses)
+                        && !cx
+                            .builder
+                            .has_capability(Capability::PhysicalStorageBufferAddresses)
+                    {
+                        cx.zombie_with_span(
+                            new_id,
+                            span,
+                            "OpTypeForwardPointer without OpCapability \
+                            Addresses or PhysicalStorageBufferAddresses",
+                        );
+                    }
                     Some(new_id)
                 }
                 // State: This is the third or more time we've seen this type, and we've already emitted an
@@ -459,7 +472,7 @@ fn trans_scalar<'tcx>(
             if let Some(predefined_result) =
                 cx.type_cache
                     .recursive_pointee_cache
-                    .begin(cx, pointee_ty, storage_class)
+                    .begin(cx, span, pointee_ty, storage_class)
             {
                 predefined_result
             } else {

crates/rustc_codegen_spirv/src/codegen_cx/mod.rs

@@ -216,6 +216,15 @@ impl<'tcx> CodegenCx<'tcx> {
             self.emit_global()
                 .variable(ty, None, StorageClass::Function, Some(initializer));
 
+        // In all likelihood, this zombie message will get overwritten in SpirvValue::def_with_span
+        // to the use site of this constant. However, if this constant happens to never get used, we
+        // still want to zobmie it, so zombie here.
+        self.zombie_even_in_user_code(
+            global_var,
+            span,
+            "Cannot use this pointer directly, it must be dereferenced first",
+        );
+
         SpirvValue {
             kind: SpirvValueKind::ConstantPointer {
                 initializer,

crates/rustc_codegen_spirv/src/spirv_type.rs

@@ -189,12 +189,16 @@ impl SpirvType {
                 storage_class,
                 pointee,
             } => {
-                // Note: pointers to functions are always illegal in SPIR-V. However, the type of a
-                // pointer to a function is sometimes used in e.g. get_fn_addr, which creates a
-                // `SpirvValueKind::ConstantPointer`. So, pointers to functions are made illegal by
-                // the fact it's impossible to create a pointer to function *value*, so the type
-                // existing is fine.
-                cx.emit_global().type_pointer(None, storage_class, pointee)
+                let result = cx.emit_global().type_pointer(None, storage_class, pointee);
+                // no pointers to functions
+                if let Self::Function { .. } = cx.lookup_type(pointee) {
+                    cx.zombie_even_in_user_code(
+                        result,
+                        def_span,
+                        "function pointer types are not allowed",
+                    )
+                }
+                result
             }
             Self::Function {
                 return_type,
@@ -229,7 +233,7 @@ impl SpirvType {
 
     /// `def_with_id` is used by the `RecursivePointeeCache` to handle `OpTypeForwardPointer`: when
     /// emitting the subsequent `OpTypePointer`, the ID is already known and must be re-used.
-    pub fn def_with_id(self, cx: &CodegenCx<'_>, _def_span: Span, id: Word) -> Word {
+    pub fn def_with_id(self, cx: &CodegenCx<'_>, def_span: Span, id: Word) -> Word {
         if let Some(cached) = cx.type_cache.get(&self) {
             assert_eq!(cached, id);
             return cached;
@@ -238,9 +242,20 @@ impl SpirvType {
             Self::Pointer {
                 storage_class,
                 pointee,
-            } => cx
-                .emit_global()
-                .type_pointer(Some(id), storage_class, pointee),
+            } => {
+                let result = cx
+                    .emit_global()
+                    .type_pointer(Some(id), storage_class, pointee);
+                // no pointers to functions
+                if let Self::Function { .. } = cx.lookup_type(pointee) {
+                    cx.zombie_even_in_user_code(
+                        result,
+                        def_span,
+                        "function pointer types are not allowed",
+                    )
+                }
+                result
+            }
             ref other => cx
                 .tcx
                 .sess

crates/spirv-builder/src/test/basic.rs

@@ -1,4 +1,23 @@
 use super::{dis_fn, val, val_vulkan};
+use std::ffi::OsStr;
+
+struct SetEnvVar<'a> {
+    k: &'a OsStr,
+}
+
+impl<'a> SetEnvVar<'a> {
+    fn new(k: &'a impl AsRef<OsStr>, v: impl AsRef<OsStr>) -> Self {
+        let k = k.as_ref();
+        std::env::set_var(k, v);
+        Self { k }
+    }
+}
+
+impl<'a> Drop for SetEnvVar<'a> {
+    fn drop(&mut self) {
+        std::env::remove_var(self.k)
+    }
+}
 
 #[test]
 fn hello_world() {
@@ -10,6 +29,19 @@ pub fn main() {
 "#);
 }
 
+#[test]
+// blocked on: https://github.com/EmbarkStudios/rust-gpu/issues/69
+#[ignore]
+fn no_dce() {
+    let _var = SetEnvVar::new(&"NO_DCE", "1");
+    val(r#"
+#[allow(unused_attributes)]
+#[spirv(fragment)]
+pub fn no_dce() {
+}
+"#);
+}
+
 #[test]
 fn add_two_ints() {
     dis_fn(