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authorBjörn Gustavsson <[email protected]>2015-10-05 06:43:12 +0200
committerBjörn Gustavsson <[email protected]>2015-10-05 12:47:55 +0200
commit76bb9f0e9a0b36ea7c9720c2bf90f6b52a4eabf8 (patch)
tree47e29acaeafb5025531d8736ffb7ded30cf678a3 /lib/compiler/src
parent7dd616c1832c54370be7f796a4b6578a8d9aedd9 (diff)
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beam_reorder: Eliminate compiler crash
c288ab87 added beam_reorder to move get_tuple_element instructions. Compiling code such as the following would crash the compiler: alloc(_U1, _U2, R) -> V = R#alloc.version, Res = id(V), _ = id(0), Res. The crash would occur because the following two instructions: {get_tuple_element,{x,2},1,{x,1}}. {allocate_zero,1,2}. were swapped and rewritten to: {allocate_zero,1,1}. {get_tuple_element,{x,2},1,{x,1}}. That transformation is not safe because the allocate_zero instruction would kill {x,2}, which is the register that is holding the reference to the tuple. Only do the transformation when the tuple reference is in an x register with a lower number than the destination register.
Diffstat (limited to 'lib/compiler/src')
-rw-r--r--lib/compiler/src/beam_reorder.erl21
1 files changed, 13 insertions, 8 deletions
diff --git a/lib/compiler/src/beam_reorder.erl b/lib/compiler/src/beam_reorder.erl
index 70adca6b04..41586a7bf2 100644
--- a/lib/compiler/src/beam_reorder.erl
+++ b/lib/compiler/src/beam_reorder.erl
@@ -110,14 +110,19 @@ reorder_1([{test,_,{f,L},Ss}=I|Is0], D0,
end
end
end;
-reorder_1([{allocate_zero,N,Live}|Is], D,
- [{get_tuple_element,_,_,{x,X}}=G|Acc])
- when X+1 =:= Live ->
- %% Move allocation instruction upwards past get_tuple_element
- %% instructions to give more opportunities for moving
- %% get_tuple_element instructions.
- I = {allocate_zero,N,X},
- reorder_1([I,G|Is], D, Acc);
+reorder_1([{allocate_zero,N,Live}=I0|Is], D,
+ [{get_tuple_element,{x,Tup},_,{x,Dst}}=G|Acc]=Acc0) ->
+ case Tup < Dst andalso Dst+1 =:= Live of
+ true ->
+ %% Move allocation instruction upwards past
+ %% get_tuple_element instructions to create more
+ %% opportunities for moving get_tuple_element
+ %% instructions.
+ I = {allocate_zero,N,Dst},
+ reorder_1([I,G|Is], D, Acc);
+ false ->
+ reorder_1(Is, D, [I0|Acc0])
+ end;
reorder_1([I|Is], D, Acc) ->
reorder_1(Is, D, [I|Acc]);
reorder_1([], _, Acc) -> reverse(Acc).