Auto merge of #48786 - nagisa:fp, r=nikomatsakis

Add force-frame-pointer flag to allow control of frame pointer ommision

Rebase of #47152 plus some changes suggested by https://github.com/rust-lang/rust/issues/48785.

Fixes #11906

r? @nikomatsakis

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: Option<bool> = (None, parse_opt_bool, [TRACKED],
+        "force use of the frame pointers"),
     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],
@@ -2965,6 +2967,10 @@ mod tests {
         opts.cg.debuginfo = Some(0xba5eba11);
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
+        opts = reference.clone();
+        opts.cg.force_frame_pointers = Some(false);
+        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

@@ -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};
@@ -658,8 +658,11 @@ impl Session {
     }
 
     pub fn must_not_eliminate_frame_pointers(&self) -> bool {
-        self.opts.debuginfo != DebugInfoLevel::NoDebugInfo
+        if let Some(x) = self.opts.cg.force_frame_pointers {
-            || !self.target.target.options.eliminate_frame_pointer
+            x
+        } else {
+            !self.target.target.options.eliminate_frame_pointer
+        }
     }
 
     /// Returns the symbol name for the registrar function,

src/librustc_target/spec/apple_ios_base.rs

@@ -98,6 +98,7 @@ pub fn opts(arch: Arch) -> Result<TargetOptions, String> {
         executables: true,
         pre_link_args,
         has_elf_tls: false,
+        eliminate_frame_pointer: false,
         // The following line is a workaround for jemalloc 4.5 being broken on
         // ios. jemalloc 5.0 is supposed to fix this.
         // see https://github.com/rust-lang/rust/issues/45262

src/librustc_target/spec/i686_apple_darwin.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
     base.stack_probes = true;
+    base.eliminate_frame_pointer = false;
 
     Ok(Target {
         llvm_target: "i686-apple-darwin".to_string(),

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,

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=y
+
+#![crate_type="lib"]
+
+// CHECK: attributes #{{.*}} "no-frame-pointer-elim"="true"
+pub fn foo() {}

src/test/run-pass/backtrace-debuginfo.rs

@@ -16,6 +16,7 @@
 // "enable" to 0 instead.
 
 // compile-flags:-g -Cllvm-args=-enable-tail-merge=0 -Cllvm-args=-opt-bisect-limit=0
+// compile-flags:-Cforce-frame-pointers=yes
 // ignore-pretty issue #37195
 // ignore-cloudabi spawning processes is not supported
 // ignore-emscripten spawning processes is not supported