auto merge of #13001 : cmr/rust/unnamed-lifetime-nocapture, r=nikomatsakis

Closes #6751

Author: bors

src/librustc/middle/trans/base.rs

@@ -246,6 +246,8 @@ fn get_extern_rust_fn(ccx: &CrateContext, inputs: &[ty::t], output: ty::t,
 pub fn decl_rust_fn(ccx: &CrateContext, has_env: bool,
                     inputs: &[ty::t], output: ty::t,
                     name: &str) -> ValueRef {
+    use middle::ty::{BrAnon, ReLateBound};
+
     let llfty = type_of_rust_fn(ccx, has_env, inputs, output);
     let llfn = decl_cdecl_fn(ccx.llmod, name, llfty, output);
 
@@ -265,7 +267,16 @@ pub fn decl_rust_fn(ccx: &CrateContext, has_env: bool,
                 unsafe {
                     llvm::LLVMAddAttribute(llarg, lib::llvm::NoAliasAttribute as c_uint);
                 }
-            }
+            },
+            // When a reference in an argument has no named lifetime, it's
+            // impossible for that reference to escape this function(ie, be
+            // returned).
+            ty::ty_rptr(ReLateBound(_, BrAnon(_)), _) => {
+                debug!("marking argument of {} as nocapture because of anonymous lifetime", name);
+                unsafe {
+                    llvm::LLVMAddAttribute(llarg, lib::llvm::NoCaptureAttribute as c_uint);
+                }
+            },
             _ => {
                 // For non-immediate arguments the callee gets its own copy of
                 // the value on the stack, so there are no aliases

src/librustc/middle/trans/callee.rs

@@ -20,7 +20,7 @@ use std::slice;
 
 use back::abi;
 use driver::session;
-use lib::llvm::{ValueRef, NoAliasAttribute, StructRetAttribute};
+use lib::llvm::{ValueRef, NoAliasAttribute, StructRetAttribute, NoCaptureAttribute};
 use lib::llvm::llvm;
 use metadata::csearch;
 use middle::trans::base;
@@ -661,9 +661,15 @@ pub fn trans_call_inner<'a>(
             llargs.push(opt_llretslot.unwrap());
         }
 
+        // start at 1, because index 0 is the return value of the llvm func
+        let mut first_arg_offset = 1;
+
         // Push the environment (or a trait object's self).
         match (llenv, llself) {
-            (Some(llenv), None) => llargs.push(llenv),
+            (Some(llenv), None) => {
+                first_arg_offset += 1;
+                llargs.push(llenv)
+            },
             (None, Some(llself)) => llargs.push(llself),
             _ => {}
         }
@@ -682,6 +688,11 @@ pub fn trans_call_inner<'a>(
         let mut attrs = Vec::new();
         if type_of::return_uses_outptr(ccx, ret_ty) {
             attrs.push((1, StructRetAttribute));
+            // The outptr can be noalias and nocapture because it's entirely
+            // invisible to the program.
+            attrs.push((1, NoAliasAttribute));
+            attrs.push((1, NoCaptureAttribute));
+            first_arg_offset += 1;
         }
 
         // The `noalias` attribute on the return value is useful to a
@@ -695,6 +706,30 @@ pub fn trans_call_inner<'a>(
             _ => {}
         }
 
+        debug!("trans_callee_inner: first_arg_offset={}", first_arg_offset);
+
+        for (idx, &t) in ty::ty_fn_args(callee_ty).iter().enumerate()
+                                                  .map(|(i, v)| (i+first_arg_offset, v)) {
+            use middle::ty::{BrAnon, ReLateBound};
+            if !type_is_immediate(ccx, t) {
+                // if it's not immediate, we have a program-invisible pointer,
+                // which it can't possibly capture
+                attrs.push((idx, NoCaptureAttribute));
+                debug!("trans_callee_inner: argument {} nocapture because it's non-immediate", idx);
+                continue;
+            }
+
+            let t_ = ty::get(t);
+            match t_.sty {
+                ty::ty_rptr(ReLateBound(_, BrAnon(_)), _) => {
+                    debug!("trans_callee_inner: argument {} nocapture because \
+                           of anonymous lifetime", idx);
+                    attrs.push((idx, NoCaptureAttribute));
+                },
+                _ => { }
+            }
+        }
+
         // Invoke the actual rust fn and update bcx/llresult.
         let (llret, b) = base::invoke(bcx,
                                       llfn,

src/test/run-pass/out-of-stack.rs

@@ -28,6 +28,7 @@ fn silent_recurse() {
 fn loud_recurse() {
     println!("hello!");
     loud_recurse();
+    black_box(()); // don't optimize this into a tail call. please.
 }
 
 fn main() {