From 99165ce1f76573729530c241036a0514ca1cf232 Mon Sep 17 00:00:00 2001
From: Adam Perry <adam.n.perry@gmail.com>
Date: Fri, 6 Dec 2019 16:09:40 -0800
Subject: [PATCH] Caller location is propagated via immediates rather than
 memory.

---
 src/librustc_codegen_ssa/mir/block.rs |  6 ++----
 src/librustc_codegen_ssa/mir/mod.rs   | 15 +++++++++++----
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs
index b33cca2ee8d..5d25f7022c5 100644
--- a/src/librustc_codegen_ssa/mir/block.rs
+++ b/src/librustc_codegen_ssa/mir/block.rs
@@ -1016,9 +1016,7 @@ fn get_caller_location(
         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 @@ fn get_caller_location(
                 caller.col_display as u32 + 1,
             ));
             OperandRef::from_const(bx, const_loc)
-        }
+        })
     }
 
     fn get_personality_slot(
diff --git a/src/librustc_codegen_ssa/mir/mod.rs b/src/librustc_codegen_ssa/mir/mod.rs
index 6be6e13cc1d..5e4da8f2125 100644
--- a/src/librustc_codegen_ssa/mir/mod.rs
+++ b/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
-- 
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