Caller location is propagated via immediates rather than memory.

Author: anp

src/librustc_codegen_ssa/mir/block.rs

@@ -1016,9 +1016,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         bx: &mut Bx,
         span: Span,
     ) -> OperandRef<'tcx, Bx::Value> {
-        if let Some(l) = self.caller_location {
-            bx.load_operand(l)
-        } else {
+        self.caller_location.unwrap_or_else(|| {
             let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
             let caller = bx.tcx().sess.source_map().lookup_char_pos(topmost.lo());
             let const_loc = bx.tcx().const_caller_location((
@@ -1027,7 +1025,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 caller.col_display as u32 + 1,
             ));
             OperandRef::from_const(bx, const_loc)
-        }
+        })
     }
 
     fn get_personality_slot(

src/librustc_codegen_ssa/mir/mod.rs

@@ -79,7 +79,7 @@ pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     per_local_var_debug_info: Option<IndexVec<mir::Local, Vec<&'tcx mir::VarDebugInfo<'tcx>>>>,
 
     /// Caller location propagated if this function has `#[track_caller]`.
-    caller_location: Option<PlaceRef<'tcx, Bx::Value>>,
+    caller_location: Option<OperandRef<'tcx, Bx::Value>>,
 }
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
@@ -434,10 +434,17 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
             fx.fn_abi.args.len(), args.len() + 1,
             "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
         );
+
         let arg = &fx.fn_abi.args.last().unwrap();
-        let place = PlaceRef::alloca(bx, arg.layout);
-        bx.store_fn_arg(arg, &mut llarg_idx, place);
-        fx.caller_location = Some(place);
+        match arg.mode {
+            PassMode::Direct(_) => (),
+            _ => panic!("caller location must be PassMode::Direct, found {:?}", arg.mode),
+        }
+
+        fx.caller_location = Some(OperandRef {
+            val: OperandValue::Immediate(bx.get_param(llarg_idx)),
+            layout: arg.layout,
+        });
     }
 
     args