Generate llvm.sideeffect at function entry instead of call

3 files changed, 9 insertions, 5 deletions

diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs
index 8e3243f5e7b..d95c0b2d87b 100644
--- a/src/librustc_codegen_ssa/mir/block.rs
+++ b/src/librustc_codegen_ssa/mir/block.rs
@@ -364,7 +364,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                  FnType::of_instance(&bx, drop_fn))
             }
         };
-        bx.sideeffect();
+        helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
         helper.do_call(self, &mut bx, fn_ty, drop_fn, args,
                        Some((ReturnDest::Nothing, target)),
                        unwind);
@@ -464,7 +464,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let fn_ty = FnType::of_instance(&bx, instance);
         let llfn = bx.get_fn(instance);
 
-        bx.sideeffect();
         // Codegen the actual panic invoke/call.
         helper.do_call(self, &mut bx, fn_ty, llfn, &args, None, cleanup);
     }
@@ -584,7 +583,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 let fn_ty = FnType::of_instance(&bx, instance);
                 let llfn = bx.get_fn(instance);
 
-                bx.sideeffect();
+                if let Some((_, target)) = destination.as_ref() {
+                    helper.maybe_sideeffect(self.mir, &mut bx, &[*target]);
+                }
                 // Codegen the actual panic invoke/call.
                 helper.do_call(
                     self,
@@ -820,7 +821,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             _ => span_bug!(span, "no llfn for call"),
         };
 
-        bx.sideeffect();
+        if let Some((_, target)) = destination.as_ref() {
+            helper.maybe_sideeffect(self.mir, &mut bx, &[*target]);
+        }
         helper.do_call(self, &mut bx, fn_ty, fn_ptr, &llargs,
                        destination.as_ref().map(|&(_, target)| (ret_dest, target)),
                        cleanup);
diff --git a/src/librustc_codegen_ssa/mir/mod.rs b/src/librustc_codegen_ssa/mir/mod.rs
index c341c0685c6..e4fdf0a09bb 100644
--- a/src/librustc_codegen_ssa/mir/mod.rs
+++ b/src/librustc_codegen_ssa/mir/mod.rs
@@ -204,6 +204,8 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         bx.set_personality_fn(cx.eh_personality());
     }
 
+    bx.sideeffect();
+
     let cleanup_kinds = analyze::cleanup_kinds(&mir);
     // Allocate a `Block` for every basic block, except
     // the start block, if nothing loops back to it.
diff --git a/src/librustc_codegen_ssa/mir/rvalue.rs b/src/librustc_codegen_ssa/mir/rvalue.rs
index 11a75c6f38c..9b69383b455 100644
--- a/src/librustc_codegen_ssa/mir/rvalue.rs
+++ b/src/librustc_codegen_ssa/mir/rvalue.rs
@@ -486,7 +486,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 };
                 let instance = ty::Instance::mono(bx.tcx(), def_id);
                 let r = bx.cx().get_fn(instance);
-                bx.sideeffect();
                 let call = bx.call(r, &[llsize, llalign], None);
                 let val = bx.pointercast(call, llty_ptr);