auto merge of #15975 : dotdash/rust/unwind_lifetimes, r=pcwalton

Currently we don't emit lifetime end markers when translating the
unwinding code. I omitted that when I added the support for lifetime
intrinsics, because I initially made the mistake of just returning true
in clean_on_unwind(). That caused almost all calls to be translated as
invokes, leading to quite awful results.

To correctly emit the lifetime end markers, we must differentiate
between cleanup that requires unwinding and such cleanup that just wants
to emit code during unwinding.

Author: bors

src/librustc/middle/trans/cleanup.rs

@@ -68,6 +68,7 @@ pub struct CachedEarlyExit {
 }
 
 pub trait Cleanup {
+    fn must_unwind(&self) -> bool;
     fn clean_on_unwind(&self) -> bool;
     fn trans<'a>(&self, bcx: &'a Block<'a>) -> &'a Block<'a>;
 }
@@ -252,7 +253,7 @@ impl<'a> CleanupMethods<'a> for FunctionContext<'a> {
         if !ty::type_needs_drop(self.ccx.tcx(), ty) { return; }
         let drop = box DropValue {
             is_immediate: false,
-            on_unwind: ty::type_needs_unwind_cleanup(self.ccx.tcx(), ty),
+            must_unwind: ty::type_needs_unwind_cleanup(self.ccx.tcx(), ty),
             val: val,
             ty: ty,
             zero: false
@@ -278,7 +279,7 @@ impl<'a> CleanupMethods<'a> for FunctionContext<'a> {
         if !ty::type_needs_drop(self.ccx.tcx(), ty) { return; }
         let drop = box DropValue {
             is_immediate: false,
-            on_unwind: ty::type_needs_unwind_cleanup(self.ccx.tcx(), ty),
+            must_unwind: ty::type_needs_unwind_cleanup(self.ccx.tcx(), ty),
             val: val,
             ty: ty,
             zero: true
@@ -304,7 +305,7 @@ impl<'a> CleanupMethods<'a> for FunctionContext<'a> {
         if !ty::type_needs_drop(self.ccx.tcx(), ty) { return; }
         let drop = box DropValue {
             is_immediate: true,
-            on_unwind: ty::type_needs_unwind_cleanup(self.ccx.tcx(), ty),
+            must_unwind: ty::type_needs_unwind_cleanup(self.ccx.tcx(), ty),
             val: val,
             ty: ty,
             zero: false
@@ -793,10 +794,10 @@ impl<'a> CleanupScope<'a> {
     }
 
     fn needs_invoke(&self) -> bool {
-        /*! True if this scope has cleanups for use during unwinding */
+        /*! True if this scope has cleanups that need unwinding */
 
         self.cached_landing_pad.is_some() ||
-            self.cleanups.iter().any(|c| c.clean_on_unwind())
+            self.cleanups.iter().any(|c| c.must_unwind())
     }
 
     fn block_name(&self, prefix: &str) -> String {
@@ -864,15 +865,19 @@ impl EarlyExitLabel {
 
 pub struct DropValue {
     is_immediate: bool,
-    on_unwind: bool,
+    must_unwind: bool,
     val: ValueRef,
     ty: ty::t,
     zero: bool
 }
 
 impl Cleanup for DropValue {
+    fn must_unwind(&self) -> bool {
+        self.must_unwind
+    }
+
     fn clean_on_unwind(&self) -> bool {
-        self.on_unwind
+        self.must_unwind
     }
 
     fn trans<'a>(&self, bcx: &'a Block<'a>) -> &'a Block<'a> {
@@ -900,6 +905,10 @@ pub struct FreeValue {
 }
 
 impl Cleanup for FreeValue {
+    fn must_unwind(&self) -> bool {
+        true
+    }
+
     fn clean_on_unwind(&self) -> bool {
         true
     }
@@ -921,10 +930,14 @@ pub struct LifetimeEnd {
 }
 
 impl Cleanup for LifetimeEnd {
-    fn clean_on_unwind(&self) -> bool {
+    fn must_unwind(&self) -> bool {
         false
     }
 
+    fn clean_on_unwind(&self) -> bool {
+        true
+    }
+
     fn trans<'a>(&self, bcx: &'a Block<'a>) -> &'a Block<'a> {
         base::call_lifetime_end(bcx, self.ptr);
         bcx