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

src/librustc/session/config.rs

@@ -1094,6 +1094,8 @@ 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],
@@ -2790,6 +2792,10 @@ mod tests {
         opts.cg.debuginfo = Some(0xba5eba11);
         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());

src/librustc/session/mod.rs

@@ -19,7 +19,7 @@ use lint;
 use middle::allocator::AllocatorKind;
 use middle::dependency_format;
 use session::search_paths::PathKind;
-use session::config::{BorrowckMode, DebugInfoLevel, OutputType, Epoch};
+use session::config::{BorrowckMode, OutputType, Epoch};
 use ty::tls;
 use util::nodemap::{FxHashMap, FxHashSet};
 use util::common::{duration_to_secs_str, ErrorReported};
@@ -613,8 +613,8 @@ impl Session {
     }
 
     pub fn must_not_eliminate_frame_pointers(&self) -> bool {
-        self.opts.debuginfo != DebugInfoLevel::NoDebugInfo ||
-        !self.target.target.options.eliminate_frame_pointer
+        self.opts.cg.force_frame_pointers ||
+            !self.target.target.options.eliminate_frame_pointer
     }
 
     /// Returns the symbol name for the registrar function,

src/librustc_trans/attributes.rs

@@ -68,8 +68,6 @@ 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,

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() {}