Don't force-enable frame pointers when generating debug info

We apparently used to generate bad/incomplete debug info causing
debuggers not to find symbols of stack allocated variables. This was
somehow worked around by having frame pointers.

With the current codegen, this seems no longer necessary, so we can
remove the code that force-enables frame pointers whenever debug info
is requested.

Since certain situations, like profiling code profit from having frame
pointers, we add a -Cforce-frame-pointers flag to always enable frame
pointers.

Fixes #11906

4 files changed, 23 insertions, 3 deletions

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 06922d986b3..023be789222 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1053,6 +1053,8 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
          2 = full debug info with variable and type information"),
     opt_level: Option<String> = (None, parse_opt_string, [TRACKED],
         "optimize with possible levels 0-3, s, or z"),
+    force_frame_pointers: bool = (false, parse_bool, [TRACKED],
+        "force frame pointers to be used"),
     debug_assertions: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "explicitly enable the cfg(debug_assertions) directive"),
     inline_threshold: Option<usize> = (None, parse_opt_uint, [TRACKED],
@@ -2966,6 +2968,10 @@ mod tests {
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
         opts = reference.clone();
+        opts.cg.force_frame_pointers = true;
+        assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
+
+        opts = reference.clone();
         opts.cg.debug_assertions = Some(true);
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 37a6b2e79f7..45b7e2d1740 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -20,7 +20,7 @@ use lint::builtin::BuiltinLintDiagnostics;
 use middle::allocator::AllocatorKind;
 use middle::dependency_format;
 use session::search_paths::PathKind;
-use session::config::{DebugInfoLevel, OutputType};
+use session::config::{OutputType};
 use ty::tls;
 use util::nodemap::{FxHashSet};
 use util::common::{duration_to_secs_str, ErrorReported};
diff --git a/src/librustc_trans/attributes.rs b/src/librustc_trans/attributes.rs
index f455c19cc0b..5baed57092d 100644
--- a/src/librustc_trans/attributes.rs
+++ b/src/librustc_trans/attributes.rs
@@ -69,8 +69,6 @@ pub fn naked(val: ValueRef, is_naked: bool) {
 }
 
 pub fn set_frame_pointer_elimination(cx: &CodegenCx, llfn: ValueRef) {
-    // FIXME: #11906: Omitting frame pointers breaks retrieving the value of a
-    // parameter.
     if cx.sess().must_not_eliminate_frame_pointers() {
         llvm::AddFunctionAttrStringValue(
             llfn, llvm::AttributePlace::Function,
diff --git a/src/test/codegen/force-frame-pointers.rs b/src/test/codegen/force-frame-pointers.rs
new file mode 100644
index 00000000000..d40406a0476
--- /dev/null
+++ b/src/test/codegen/force-frame-pointers.rs
@@ -0,0 +1,16 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// compile-flags: -C no-prepopulate-passes -C force-frame-pointers
+
+#![crate_type="lib"]
+
+// CHECK: attributes #{{.*}} "no-frame-pointer-elim"="true"
+pub fn foo() {}