[AVR] Correctly set the pointer address space when constructing pointers to functions

This patch extends the existing `type_i8p` method so that it requires an
explicit address space to be specified. Before this patch, the
`type_i8p` method implcitily assumed the default address space, which is
not a safe transformation on all targets, namely AVR.

The Rust compiler already has support for tracking the "instruction
address space" on a per-target basis. This patch extends the code
generation routines so that an address space must always be specified.

In my estimation, around 15% of the callers of `type_i8p` produced
invalid code on AVR due to the loss of address space prior to LLVM final
code generation. This would lead to unavoidable assertion errors
relating to invalid bitcasts.

With this patch, the address space is always either 1) explicitly set to
the instruction address space because the logic is dealing with functions
which must be placed there, or 2) explicitly set to the default address
space 0 because the logic can only operate on data space pointers and thus
we keep the existing semantics of assuming the default, "data" address space.

3 files changed, 12 insertions, 4 deletions

diff --git a/src/librustc_codegen_ssa/meth.rs b/src/librustc_codegen_ssa/meth.rs
index cfa01280e5a..bcc19c6a44b 100644
--- a/src/librustc_codegen_ssa/meth.rs
+++ b/src/librustc_codegen_ssa/meth.rs
@@ -75,7 +75,7 @@ pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
     }
 
     // Not in the cache; build it.
-    let nullptr = cx.const_null(cx.type_i8p());
+    let nullptr = cx.const_null(cx.type_i8p_ext(cx.data_layout().instruction_address_space));
 
     let methods_root;
     let methods = if let Some(trait_ref) = trait_ref {
diff --git a/src/librustc_codegen_ssa/mir/mod.rs b/src/librustc_codegen_ssa/mir/mod.rs
index 00b4bf96afa..f4d83e87710 100644
--- a/src/librustc_codegen_ssa/mir/mod.rs
+++ b/src/librustc_codegen_ssa/mir/mod.rs
@@ -6,6 +6,7 @@ use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
 use rustc_target::abi::call::{FnAbi, PassMode};
+use rustc_target::abi::HasDataLayout;
 
 use std::iter;
 
@@ -323,7 +324,9 @@ fn create_funclets<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                     // C++ personality function, but `catch (...)` has no type so
                     // it's null. The 64 here is actually a bitfield which
                     // represents that this is a catch-all block.
-                    let null = bx.const_null(bx.type_i8p());
+                    let null = bx.const_null(
+                        bx.type_i8p_ext(bx.cx().data_layout().instruction_address_space),
+                    );
                     let sixty_four = bx.const_i32(64);
                     funclet = cp_bx.catch_pad(cs, &[null, sixty_four, null]);
                     cp_bx.br(llbb);
diff --git a/src/librustc_codegen_ssa/traits/type_.rs b/src/librustc_codegen_ssa/traits/type_.rs
index c55bf9858b9..726d948cfd4 100644
--- a/src/librustc_codegen_ssa/traits/type_.rs
+++ b/src/librustc_codegen_ssa/traits/type_.rs
@@ -7,7 +7,7 @@ use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::DUMMY_SP;
 use rustc_target::abi::call::{ArgAbi, CastTarget, FnAbi, Reg};
-use rustc_target::abi::Integer;
+use rustc_target::abi::{AddressSpace, Integer};
 
 // This depends on `Backend` and not `BackendTypes`, because consumers will probably want to use
 // `LayoutOf` or `HasTyCtxt`. This way, they don't have to add a constraint on it themselves.
@@ -27,6 +27,7 @@ pub trait BaseTypeMethods<'tcx>: Backend<'tcx> {
     fn type_struct(&self, els: &[Self::Type], packed: bool) -> Self::Type;
     fn type_kind(&self, ty: Self::Type) -> TypeKind;
     fn type_ptr_to(&self, ty: Self::Type) -> Self::Type;
+    fn type_ptr_to_ext(&self, ty: Self::Type, address_space: AddressSpace) -> Self::Type;
     fn element_type(&self, ty: Self::Type) -> Self::Type;
 
     /// Returns the number of elements in `self` if it is a LLVM vector type.
@@ -42,7 +43,11 @@ pub trait BaseTypeMethods<'tcx>: Backend<'tcx> {
 
 pub trait DerivedTypeMethods<'tcx>: BaseTypeMethods<'tcx> + MiscMethods<'tcx> {
     fn type_i8p(&self) -> Self::Type {
-        self.type_ptr_to(self.type_i8())
+        self.type_i8p_ext(AddressSpace::DATA)
+    }
+
+    fn type_i8p_ext(&self, address_space: AddressSpace) -> Self::Type {
+        self.type_ptr_to_ext(self.type_i8(), address_space)
     }
 
     fn type_int(&self) -> Self::Type {