Generate llvm.sideeffect at function entry instead of call

Author: sfanxiang

src/librustc_codegen_llvm/intrinsic.rs

@@ -124,7 +124,6 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                 self.call(expect, &[args[0].immediate(), self.const_bool(false)], None)
             }
             "try" => {
-                self.sideeffect();
                 try_intrinsic(self,
                               args[0].immediate(),
                               args[1].immediate(),
@@ -818,6 +817,7 @@ fn codegen_msvc_try(
 ) {
     let llfn = get_rust_try_fn(bx, &mut |mut bx| {
         bx.set_personality_fn(bx.eh_personality());
+        bx.sideeffect();
 
         let mut normal = bx.build_sibling_block("normal");
         let mut catchswitch = bx.build_sibling_block("catchswitch");
@@ -941,6 +941,8 @@ fn codegen_gnu_try(
         // expected to be `*mut *mut u8` for this to actually work, but that's
         // managed by the standard library.
 
+        bx.sideeffect();
+
         let mut then = bx.build_sibling_block("then");
         let mut catch = bx.build_sibling_block("catch");
 

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);

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.

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);