Auto merge of #65881 - anp:implicit-caller-location, r=eddyb,oli-obk

Implement #[track_caller] attribute. (RFC 2091 4/N)

Implements the `#[track_caller]` attribute in both const and codegen contexts.

The const implementation walks up the stack to find the nearest untracked callsite.

The codegen implementation adds an implicit argument to tracked function calls, and populates it with either a call to the previously-landed intrinsic or if the caller has `#[track_caller]` with a copy of the location passed to the current function.

Also includes a little cleanup and a few comments in the other caller location areas.

[Depends on: 65664](https://github.com/rust-lang/rust/pull/65664)
[RFC 2091 text](https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md)
[Tracking issue](https://github.com/rust-lang/rust/issues/47809)
[Tracking doc](https://paper.dropbox.com/doc/track_rfc_2091_impl-notes--Anf1NwnIb0xcRv31YLIadyj0Ag-rwCdRc2fi2yvRZ7syGZ9q#:uid=863513134494965680023183&h2=TODO-actually-pass-location-to)

2 files changed, 50 insertions, 12 deletions

diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs
index ce703f24335..e68349660ba 100644
--- a/src/librustc_codegen_ssa/mir/block.rs
+++ b/src/librustc_codegen_ssa/mir/block.rs
@@ -774,6 +774,18 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 &fn_abi.args[first_args.len()..])
         }
 
+        let needs_location =
+            instance.map_or(false, |i| i.def.requires_caller_location(self.cx.tcx()));
+        if needs_location {
+            assert_eq!(
+                fn_abi.args.len(), args.len() + 1,
+                "#[track_caller] fn's must have 1 more argument in their ABI than in their MIR",
+            );
+            let location = self.get_caller_location(&mut bx, span);
+            let last_arg = fn_abi.args.last().unwrap();
+            self.codegen_argument(&mut bx, location, &mut llargs, last_arg);
+        }
+
         let fn_ptr = match (llfn, instance) {
             (Some(llfn), _) => llfn,
             (None, Some(instance)) => bx.get_fn_addr(instance),
@@ -1010,14 +1022,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         bx: &mut Bx,
         span: Span,
     ) -> OperandRef<'tcx, Bx::Value> {
-        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((
-            Symbol::intern(&caller.file.name.to_string()),
-            caller.line as u32,
-            caller.col_display as u32 + 1,
-        ));
-        OperandRef::from_const(bx, const_loc)
+        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((
+                Symbol::intern(&caller.file.name.to_string()),
+                caller.line as u32,
+                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 3a157ca24a4..33e343de86b 100644
--- a/src/librustc_codegen_ssa/mir/mod.rs
+++ b/src/librustc_codegen_ssa/mir/mod.rs
@@ -77,6 +77,9 @@ pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     /// All `VarDebuginfo` from the MIR body, partitioned by `Local`.
     /// This is `None` if no variable debuginfo/names are needed.
     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<OperandRef<'tcx, Bx::Value>>,
 }
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
@@ -172,13 +175,14 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         locals: IndexVec::new(),
         debug_context,
         per_local_var_debug_info: debuginfo::per_local_var_debug_info(cx.tcx(), mir_body),
+        caller_location: None,
     };
 
     let memory_locals = analyze::non_ssa_locals(&fx);
 
     // Allocate variable and temp allocas
     fx.locals = {
-        let args = arg_local_refs(&mut bx, &fx, &memory_locals);
+        let args = arg_local_refs(&mut bx, &mut fx, &memory_locals);
 
         let mut allocate_local = |local| {
             let decl = &mir_body.local_decls[local];
@@ -320,14 +324,14 @@ fn create_funclets<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 /// indirect.
 fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     bx: &mut Bx,
-    fx: &FunctionCx<'a, 'tcx, Bx>,
+    fx: &mut FunctionCx<'a, 'tcx, Bx>,
     memory_locals: &BitSet<mir::Local>,
 ) -> Vec<LocalRef<'tcx, Bx::Value>> {
     let mir = fx.mir;
     let mut idx = 0;
     let mut llarg_idx = fx.fn_abi.ret.is_indirect() as usize;
 
-    mir.args_iter().enumerate().map(|(arg_index, local)| {
+    let args = mir.args_iter().enumerate().map(|(arg_index, local)| {
         let arg_decl = &mir.local_decls[local];
 
         if Some(local) == mir.spread_arg {
@@ -423,7 +427,27 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
             bx.store_fn_arg(arg, &mut llarg_idx, tmp);
             LocalRef::Place(tmp)
         }
-    }).collect()
+    }).collect::<Vec<_>>();
+
+    if fx.instance.def.requires_caller_location(bx.tcx()) {
+        assert_eq!(
+            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();
+        match arg.mode {
+            PassMode::Direct(_) => (),
+            _ => bug!("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
 }
 
 mod analyze;