diff --git a/src/ctx.rs b/src/ctx.rs
index e40669c14f..35e0e72798 100644
--- a/src/ctx.rs
+++ b/src/ctx.rs
@@ -4,15 +4,35 @@ use local_tracker::LocalTracker;
 use rspirv::binary::Assemble;
 use rspirv::dr::Builder;
 use rspirv::spirv::{AddressingModel, Capability, MemoryModel, StorageClass, Word};
-use rustc_middle::mir::BasicBlock;
-use rustc_middle::ty::{subst::SubstsRef, TyCtxt};
+use rustc_middle::mir::{BasicBlock, Body};
+use rustc_middle::ty::subst::SubstsRef;
+use rustc_middle::ty::{fold::TypeFoldable, Instance, ParamEnv, TyCtxt};
+use rustc_span::def_id::DefId;
 use std::collections::HashMap;
 use std::hash::Hash;
 
+#[derive(Copy, Clone)]
+pub enum PointerSize {
+    P32,
+    P64,
+}
+
+impl PointerSize {
+    pub fn val(self) -> u64 {
+        match self {
+            PointerSize::P32 => 32,
+            PointerSize::P64 => 64,
+        }
+    }
+}
+
+/// Context is the "bag of random variables" used for global state - i.e. variables that live the whole compilation.
 pub struct Context<'tcx> {
     pub tcx: TyCtxt<'tcx>,
     pub spirv: Builder,
     spirv_helper: SpirvHelper,
+    pub pointer_size: PointerSize,
+    func_defs: ForwardReference<(DefId, SubstsRef<'tcx>)>,
 }
 
 impl<'tcx> Context<'tcx> {
@@ -22,54 +42,92 @@ impl<'tcx> Context<'tcx> {
         // Temp hack: Linkage allows us to get away with no OpEntryPoint
         spirv.capability(Capability::Linkage);
         spirv.memory_model(AddressingModel::Logical, MemoryModel::GLSL450);
+        let _ = PointerSize::P32; // just mark as used
         Self {
             tcx,
             spirv,
             spirv_helper: SpirvHelper::new(),
+            pointer_size: PointerSize::P64,
+            func_defs: ForwardReference::new(),
         }
     }
 
     pub fn assemble(self) -> Vec<u32> {
         self.spirv.module().assemble()
     }
+
+    pub fn get_func_def(&mut self, id: DefId, substs: SubstsRef<'tcx>) -> Word {
+        self.func_defs.get(&mut self.spirv, (id, substs))
+    }
 }
 
+/// FnCtx is the "bag of random variables" used for state when compiling a particular function - i.e. variables that are
+/// specific to compiling a particular function. Note it carries a reference to the global Context, so those variables
+/// can be accessed too.
 pub struct FnCtx<'ctx, 'tcx> {
+    /// The global state - note this field is `pub`, so if needed, you can go through this field, instead of the helper
+    /// functions, to satisfy the borrow checker (since using the helper functions borrow this whole struct).
     pub ctx: &'ctx mut Context<'tcx>,
-    pub substs: SubstsRef<'tcx>,
+    pub instance: Instance<'tcx>,
+    pub body: &'tcx Body<'tcx>,
     pub is_void: bool,
     basic_blocks: ForwardReference<BasicBlock>,
     pub locals: LocalTracker,
 }
 
 impl<'ctx, 'tcx> FnCtx<'ctx, 'tcx> {
-    pub fn new(ctx: &'ctx mut Context<'tcx>, substs: SubstsRef<'tcx>) -> Self {
+    pub fn new(
+        ctx: &'ctx mut Context<'tcx>,
+        instance: Instance<'tcx>,
+        body: &'tcx Body<'tcx>,
+    ) -> Self {
         Self {
             ctx,
-            substs,
+            instance,
+            body,
             is_void: false,
             basic_blocks: ForwardReference::new(),
             locals: LocalTracker::new(),
         }
     }
 
+    /*
     pub fn tcx(&mut self) -> &mut TyCtxt<'tcx> {
         &mut self.ctx.tcx
     }
+    */
 
     pub fn spirv(&mut self) -> &mut Builder {
         &mut self.ctx.spirv
     }
 
+    /// Gets the spir-v label for a basic block, or generates one if it doesn't exist.
     pub fn get_basic_block(&mut self, bb: BasicBlock) -> Word {
         self.basic_blocks.get(&mut self.ctx.spirv, bb)
     }
 
+    /// rspirv doesn't cache type_pointer, so cache it ourselves here.
     pub fn type_pointer(&mut self, pointee_type: Word) -> Word {
         self.ctx
             .spirv_helper
             .type_pointer(&mut self.ctx.spirv, pointee_type)
     }
+
+    // copied from rustc_codegen_cranelift
+    pub(crate) fn monomorphize<T>(&self, value: &T) -> T
+    where
+        T: TypeFoldable<'tcx> + Copy,
+    {
+        if let Some(substs) = self.instance.substs_for_mir_body() {
+            self.ctx
+                .tcx
+                .subst_and_normalize_erasing_regions(substs, ParamEnv::reveal_all(), value)
+        } else {
+            self.ctx
+                .tcx
+                .normalize_erasing_regions(ParamEnv::reveal_all(), *value)
+        }
+    }
 }
 
 struct ForwardReference<T: Eq + Hash> {
diff --git a/src/ctx/local_tracker.rs b/src/ctx/local_tracker.rs
index 5989f311f7..7fcf5b0706 100644
--- a/src/ctx/local_tracker.rs
+++ b/src/ctx/local_tracker.rs
@@ -26,7 +26,8 @@ impl LocalTracker {
     }
 
     pub fn get(&self, local: Local) -> Word {
-        // This probably needs to be fixed, forward-references might be a thing
+        // This probably needs to be fixed, forward-references might be a thing.
+        // (MIR probably declares all locals up front, so use that?)
         *self.locals.get(&local).expect("Undefined local")
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index e6ad87f558..148fea7266 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -114,6 +114,7 @@ impl CodegenBackend for TheBackend {
         _sess: &Session,
         _dep_graph: &DepGraph,
     ) -> Result<Box<dyn Any>, ErrorReported> {
+        // I think this function is if `codegen_crate` spawns threads, this is supposed to join those threads?
         Ok(ongoing_codegen)
         // let crate_name = ongoing_codegen
         //     .downcast::<Symbol>()
diff --git a/src/trans.rs b/src/trans.rs
index 9a0a2ba6e2..0b147d66cc 100644
--- a/src/trans.rs
+++ b/src/trans.rs
@@ -1,14 +1,9 @@
 use crate::ctx::{Context, FnCtx};
 use rspirv::spirv::{FunctionControl, Word};
-use rustc_middle::mir::{
-    Body, Operand, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
-};
-use rustc_middle::ty::{Ty, TyKind};
+use rustc_middle::mir::{Operand, Rvalue, Statement, StatementKind, Terminator, TerminatorKind};
+use rustc_middle::ty::{Instance, ParamEnv, Ty, TyKind};
 
-pub fn trans_fn<'ctx, 'tcx>(
-    ctx: &'ctx mut Context<'tcx>,
-    instance: rustc_middle::ty::Instance<'tcx>,
-) {
+pub fn trans_fn<'ctx, 'tcx>(ctx: &'ctx mut Context<'tcx>, instance: Instance<'tcx>) {
     {
         let mut mir = ::std::io::Cursor::new(Vec::new());
 
@@ -20,13 +15,13 @@ pub fn trans_fn<'ctx, 'tcx>(
         println!("{}", s);
     }
 
-    let mir = ctx.tcx.optimized_mir(instance.def_id());
+    let body = ctx.tcx.optimized_mir(instance.def_id());
 
-    let mut fnctx = FnCtx::new(ctx, instance.substs);
+    let mut fnctx = FnCtx::new(ctx, instance, body);
 
-    trans_fn_header(&mut fnctx, mir);
+    trans_fn_header(&mut fnctx);
 
-    for (bb, bb_data) in mir.basic_blocks().iter_enumerated() {
+    for (bb, bb_data) in fnctx.body.basic_blocks().iter_enumerated() {
         let label_id = fnctx.get_basic_block(bb);
         fnctx.spirv().begin_block(Some(label_id)).unwrap();
 
@@ -38,17 +33,16 @@ pub fn trans_fn<'ctx, 'tcx>(
     fnctx.spirv().end_function().unwrap();
 }
 
-// return_type, fn_type
-fn trans_fn_header<'tcx>(ctx: &mut FnCtx, body: &Body<'tcx>) {
-    let mir_return_type = body.local_decls[0u32.into()].ty;
+fn trans_fn_header<'tcx>(ctx: &mut FnCtx<'_, 'tcx>) {
+    let mir_return_type = ctx.body.local_decls[0u32.into()].ty;
     let return_type = trans_type(ctx, mir_return_type);
     ctx.is_void = if let TyKind::Tuple(fields) = &mir_return_type.kind {
         fields.len() == 0
     } else {
         false
     };
-    let params = (0..body.arg_count)
-        .map(|i| trans_type(ctx, body.local_decls[(i + 1).into()].ty))
+    let params = (0..ctx.body.arg_count)
+        .map(|i| trans_type(ctx, ctx.body.local_decls[(i + 1).into()].ty))
         .collect::<Vec<_>>();
     let mut params_nonzero = params.clone();
     if params_nonzero.is_empty() {
@@ -56,12 +50,13 @@ fn trans_fn_header<'tcx>(ctx: &mut FnCtx, body: &Body<'tcx>) {
         params_nonzero.push(ctx.spirv().type_void());
     }
     let function_type = ctx.spirv().type_function(return_type, params_nonzero);
-    let function_id = None;
+    let function_id = ctx
+        .ctx
+        .get_func_def(ctx.instance.def_id(), ctx.instance.substs);
     let control = FunctionControl::NONE;
-    // TODO: keep track of function IDs
     let _ = ctx
         .spirv()
-        .begin_function(return_type, function_id, control, function_type)
+        .begin_function(return_type, Some(function_id), control, function_type)
         .unwrap();
 
     for (i, &param_type) in params.iter().enumerate() {
@@ -70,16 +65,18 @@ fn trans_fn_header<'tcx>(ctx: &mut FnCtx, body: &Body<'tcx>) {
     }
 }
 
-fn trans_type<'tcx>(ctx: &mut FnCtx, ty: Ty<'tcx>) -> Word {
-    match ty.kind {
+fn trans_type<'tcx>(ctx: &mut FnCtx<'_, 'tcx>, ty: Ty<'tcx>) -> Word {
+    let mono = ctx.monomorphize(&ty);
+    match mono.kind {
+        TyKind::Param(param) => panic!("TyKind::Param after monomorphize: {:?}", param),
         TyKind::Bool => ctx.spirv().type_bool(),
         TyKind::Tuple(fields) if fields.len() == 0 => ctx.spirv().type_void(),
         TyKind::Int(ty) => {
-            let size = ty.bit_width().expect("isize not supported yet");
+            let size = ty.bit_width().unwrap_or_else(|| ctx.ctx.pointer_size.val());
             ctx.spirv().type_int(size as u32, 1)
         }
         TyKind::Uint(ty) => {
-            let size = ty.bit_width().expect("isize not supported yet");
+            let size = ty.bit_width().unwrap_or_else(|| ctx.ctx.pointer_size.val());
             ctx.spirv().type_int(size as u32, 0)
         }
         TyKind::Float(ty) => ctx.spirv().type_float(ty.bit_width() as u32),
@@ -116,7 +113,7 @@ fn trans_stmt<'tcx>(ctx: &mut FnCtx, stmt: &Statement<'tcx>) {
     }
 }
 
-fn trans_terminator<'tcx>(ctx: &mut FnCtx, term: &Terminator<'tcx>) {
+fn trans_terminator<'tcx>(ctx: &mut FnCtx<'_, 'tcx>, term: &Terminator<'tcx>) {
     match term.kind {
         TerminatorKind::Return => {
             if ctx.is_void {
@@ -138,6 +135,47 @@ fn trans_terminator<'tcx>(ctx: &mut FnCtx, term: &Terminator<'tcx>) {
             let inst_id = ctx.get_basic_block(target);
             ctx.spirv().branch(inst_id).unwrap();
         }
+        TerminatorKind::Call {
+            ref func,
+            ref args,
+            ref destination,
+            ..
+        } => {
+            let destination = destination.expect("Divergent function calls not supported yet");
+            let fn_ty = ctx.monomorphize(&func.ty(ctx.body, ctx.ctx.tcx));
+            let fn_sig = ctx.ctx.tcx.normalize_erasing_late_bound_regions(
+                ParamEnv::reveal_all(),
+                &fn_ty.fn_sig(ctx.ctx.tcx),
+            );
+            let fn_return_type = ParamEnv::reveal_all().and(fn_sig.output()).value;
+            let result_type = trans_type(ctx, fn_return_type);
+            let function = match func {
+                // TODO: Can constant.literal.val not be a ZST?
+                Operand::Constant(constant) => match constant.literal.ty.kind {
+                    TyKind::FnDef(id, substs) => ctx.ctx.get_func_def(id, substs),
+                    ref thing => panic!("Unknown type in fn call: {:?}", thing),
+                },
+                thing => panic!("Dynamic calls not supported yet: {:?}", thing),
+            };
+            let arguments = args
+                .iter()
+                .map(|arg| trans_operand(ctx, arg))
+                .collect::<Vec<_>>();
+            let dest_local = destination.0.local;
+            if destination.0.projection.len() != 0 {
+                panic!(
+                    "Place projections aren't supported yet (fn call): {:?}",
+                    destination.0.projection
+                );
+            }
+            let result = ctx
+                .spirv()
+                .function_call(result_type, None, function, arguments)
+                .unwrap();
+            ctx.locals.def(dest_local, result);
+            let destination_bb = ctx.get_basic_block(destination.1);
+            ctx.spirv().branch(destination_bb).unwrap();
+        }
         ref thing => panic!("Unknown terminator: {:?}", thing),
     }
 }