Add `push_ctxt` instrumentation to all functions that might call `base::zero_mem`.

(Instrumentation work for Issue 22536.)

src/librustc_trans/trans/_match.rs

@@ -1499,6 +1499,7 @@ pub fn store_local<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     fn create_dummy_locals<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
                                        pat: &ast::Pat)
                                        -> Block<'blk, 'tcx> {
+        let _icx = push_ctxt("create_dummy_locals");
         // create dummy memory for the variables if we have no
         // value to store into them immediately
         let tcx = bcx.tcx();

src/librustc_trans/trans/cleanup.rs

@@ -1007,6 +1007,7 @@ fn trans<'blk>(&self,
                    bcx: Block<'blk, 'tcx>,
                    debug_loc: DebugLoc)
                    -> Block<'blk, 'tcx> {
+        let _icx = base::push_ctxt("<DropValue as Cleanup>::trans");
         let bcx = if self.is_immediate {
             glue::drop_ty_immediate(bcx, self.val, self.ty, debug_loc)
         } else {

src/librustc_trans/trans/datum.rs

@@ -311,6 +311,7 @@ fn post_store<'blk, 'tcx>(&self,
                               val: ValueRef,
                               ty: Ty<'tcx>)
                               -> Block<'blk, 'tcx> {
+        let _icx = push_ctxt("<Lvalue as KindOps>::post_store");
         if type_needs_drop(bcx.tcx(), ty) {
             // cancel cleanup of affine values by zeroing out
             let () = zero_mem(bcx, val, ty);

src/librustc_trans/trans/intrinsic.rs

@@ -156,6 +156,8 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
     let ccx = fcx.ccx;
     let tcx = bcx.tcx();
 
+    let _icx = push_ctxt("trans_intrinsic_call");
+
     let ret_ty = match callee_ty.sty {
         ty::ty_bare_fn(_, ref f) => {
             ty::erase_late_bound_regions(bcx.tcx(), &f.sig.output())