8 files changed, 51 insertions, 3 deletions
diff --git a/lib/compiler/src/beam_disasm.erl b/lib/compiler/src/beam_disasm.erl
index 8fd0b36d05..5858b14409 100644
--- a/lib/compiler/src/beam_disasm.erl
+++ b/lib/compiler/src/beam_disasm.erl
@@ -1165,6 +1165,13 @@ resolve_inst({get_map_elements,Args0},_,_,_) ->
     {get_map_elements,FLbl,Src,{list,List}};
 
 %%
+%% OTP 21.
+%%
+
+resolve_inst({build_stacktrace,[]},_,_,_) ->
+    build_stacktrace;
+
+%%
 %% Catches instructions that are not yet handled.
 %%
 resolve_inst(X,_,_,_) -> ?exit({resolve_inst,X}).
diff --git a/lib/compiler/src/beam_disasm.hrl b/lib/compiler/src/beam_disasm.hrl
index d968cd9587..8cc0bcf99b 100644
--- a/lib/compiler/src/beam_disasm.hrl
+++ b/lib/compiler/src/beam_disasm.hrl
@@ -26,7 +26,8 @@
 %%      IT SHOULD BE MOVED TO A FILE THAT DEFINES (AND EXPORTS)
 %%      PROPER TYPES FOR THE SET OF BEAM INSTRUCTIONS.
 %%
--type beam_instr() :: 'bs_init_writable' | 'fclearerror' | 'if_end'
+-type beam_instr() :: 'bs_init_writable' | 'build_stacktrace'
+                    | 'fclearerror' | 'if_end'
                     | 'remove_message' | 'return' | 'send' | 'timeout'
                     | tuple().  %% XXX: Very underspecified - FIX THIS
 
diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index dd7ec4da96..1b2a2827cb 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -781,6 +781,8 @@ live_opt([{block,Bl0}|Is], Regs0, D, Acc) ->
     {Bl,Regs} = live_opt_block(reverse(Bl0), Regs0, D, [Live0]),
     Live = {'%live',live_regs(Regs),Regs},
     live_opt(Is, Regs, D, [{block,[Live|Bl]}|Acc]);
+live_opt([build_stacktrace=I|Is], _, D, Acc) ->
+    live_opt(Is, live_call(1), D, [I|Acc]);
 live_opt([{label,L}=I|Is], Regs, D0, Acc) ->
     D = gb_trees:insert(L, Regs, D0),
     live_opt(Is, Regs, D, [I|Acc]);
diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index be8908dd6b..77f9fcebad 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -294,6 +294,8 @@ valfun_1({bs_context_to_binary,Ctx}, #vst{current=#st{x=Xs}}=Vst) ->
     end;
 valfun_1(bs_init_writable=I, Vst) ->
     call(I, 1, Vst);
+valfun_1(build_stacktrace=I, Vst) ->
+    call(I, 1, Vst);
 valfun_1({move,{y,_}=Src,{y,_}=Dst}, Vst) ->
     %% The stack trimming optimization may generate a move from an initialized
     %% but unassigned Y register to another Y register.
diff --git a/lib/compiler/src/genop.tab b/lib/compiler/src/genop.tab
index b5688de339..397e478e1e 100755
--- a/lib/compiler/src/genop.tab
+++ b/lib/compiler/src/genop.tab
@@ -545,3 +545,12 @@ BEAM_FORMAT_NUMBER=0
 ##      Test the arity of Reg and jumps to Lbl if it is not N.
 ##      Test the first element of the tuple and jumps to Lbl if it is not Atom.
 159: is_tagged_tuple/4
+
+# OTP 21
+
+## @spec build_stacktrace
+## @doc  Given the raw stacktrace in x(0), build a cooked stacktrace suitable
+##       for human consumption. Store it in x(0). Destroys all other registers.
+##       Do a garbage collection if necessary to allocate space on the heap
+##       for the result.
+160: build_stacktrace/0
diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index df880ff784..6da68f1f4e 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -415,6 +415,8 @@ expr(#c_call{module=M0,name=N0}=Call0, Ctxt, Sub) ->
 	no -> call(Call, M1, N1, Sub);
 	{yes,Seq} -> expr(Seq, Ctxt, Sub)
     end;
+expr(#c_primop{name=#c_literal{val=build_stacktrace}}, effect, _Sub) ->
+    void();
 expr(#c_primop{args=As0}=Prim, _, Sub) ->
     As1 = expr_list(As0, value, Sub),
     Prim#c_primop{args=As1};
diff --git a/lib/compiler/src/v3_codegen.erl b/lib/compiler/src/v3_codegen.erl
index 535c0679d8..9bcd6987bf 100644
--- a/lib/compiler/src/v3_codegen.erl
+++ b/lib/compiler/src/v3_codegen.erl
@@ -1656,6 +1656,11 @@ internal_cg(bs_init_writable=I, As, Rs, Le, Vdb, Bef, St) ->
     {Sis,Int} = cg_setup_call(As, Bef, Le#l.i, Vdb),
     Reg = load_vars(Rs, clear_regs(Int#sr.reg)),
     {Sis++[I],clear_dead(Int#sr{reg=Reg}, Le#l.i, Vdb),St};
+internal_cg(build_stacktrace=I, As, Rs, Le, Vdb, Bef, St) ->
+    %% This behaves like a function call.
+    {Sis,Int} = cg_setup_call(As, Bef, Le#l.i, Vdb),
+    Reg = load_vars(Rs, clear_regs(Int#sr.reg)),
+    {Sis++[I],clear_dead(Int#sr{reg=Reg}, Le#l.i, Vdb),St};
 internal_cg(raise, As, Rs, Le, Vdb, Bef, St) ->
     %% raise can be treated like a guard BIF.
     bif_cg(raise, As, Rs, Le, Vdb, Bef, St).
diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 20cb3343fb..cc8ea475d2 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -920,8 +920,9 @@ try_exception(Ecs0, St0) ->
     %% Note that Tag is not needed for rethrow - it is already in Info.
     {Evs,St1} = new_vars(3, St0), % Tag, Value, Info
     {Ecs1,Ceps,St2} = clauses(Ecs0, St1),
+    Ecs2 = try_build_stacktrace(Ecs1, hd(Evs)),
     [_,Value,Info] = Evs,
-    LA = case Ecs1 of
+    LA = case Ecs2 of
 	     [] -> [];
 	     [C|_] -> get_lineno_anno(C)
 	 end,
@@ -930,7 +931,7 @@ try_exception(Ecs0, St0) ->
 		  body=[#iprimop{anno=#a{},       %Must have an #a{}
 				 name=#c_literal{val=raise},
 				 args=[Info,Value]}]},
-    Hs = [#icase{anno=#a{anno=LA},args=[c_tuple(Evs)],clauses=Ecs1,fc=Ec}],
+    Hs = [#icase{anno=#a{anno=LA},args=[c_tuple(Evs)],clauses=Ecs2,fc=Ec}],
     {Evs,Ceps++Hs,St2}.
 
 try_after(As, St0) ->
@@ -946,6 +947,25 @@ try_after(As, St0) ->
     Hs = [#icase{anno=#a{},args=[c_tuple(Evs)],clauses=[],fc=Ec}],
     {Evs,Hs,St1}.
 
+try_build_stacktrace([#iclause{pats=Ps0,body=B0}=C0|Cs], RawStk) ->
+    [#c_tuple{es=[Class,Exc,Stk]}=Tup] = Ps0,
+    case Stk of
+        #c_var{name='_'} ->
+            %% Stacktrace variable is not used. Nothing to do.
+            [C0|try_build_stacktrace(Cs, RawStk)];
+        _ ->
+            %% Add code to build the stacktrace.
+            Ps = [Tup#c_tuple{es=[Class,Exc,RawStk]}],
+            Call = #iprimop{anno=#a{},
+                            name=#c_literal{val=build_stacktrace},
+                            args=[RawStk]},
+            Iset = #iset{var=Stk,arg=Call},
+            B = [Iset|B0],
+            C = C0#iclause{pats=Ps,body=B},
+            [C|try_build_stacktrace(Cs, RawStk)]
+    end;
+try_build_stacktrace([], _) -> [].
+
 %% expr_bin([ArgExpr], St) -> {[Arg],[PreExpr],St}.
 %%  Flatten the arguments of a bin. Do this straight left to right!
 %%  Note that ibinary needs to have its annotation wrapped in a #a{}