aboutsummaryrefslogtreecommitdiffstats
path: root/bootstrap/lib
diff options
context:
space:
mode:
authorBjörn Gustavsson <[email protected]>2017-08-29 18:02:58 +0200
committerBjörn Gustavsson <[email protected]>2017-08-31 10:11:24 +0200
commit00c13ed24a08799ba938a64e3198e75f07329486 (patch)
tree6f66bd4fe10da017d269eb1f15b80d082e3c7f66 /bootstrap/lib
parentf0b2ac51019181cc765b55e95b2723f5ed03d3fa (diff)
downloadotp-00c13ed24a08799ba938a64e3198e75f07329486.tar.gz
otp-00c13ed24a08799ba938a64e3198e75f07329486.tar.bz2
otp-00c13ed24a08799ba938a64e3198e75f07329486.zip
Eliminate unnecessary 'move' instructions
The compiler could sometimes emit unnecessary 'move' instructions in the code for binary matching, for example for this function: escape(<<Byte, Rest/bits>>, Pos) when Byte >= 127 -> escape(Rest, Pos + 1); escape(<<Byte, Rest/bits>>, Pos) -> escape(Rest, Pos + Byte); escape(<<_Rest/bits>>, Pos) -> Pos. The generated code would look like this: {function, escape, 2, 2}. {label,1}. {line,[{location,"t.erl",17}]}. {func_info,{atom,t},{atom,escape},2}. {label,2}. {test,bs_start_match2,{f,1},2,[{x,0},0],{x,0}}. {test,bs_get_integer2, {f,4}, 2, [{x,0}, {integer,8}, 1, {field_flags,[{anno,[17,{file,"t.erl"}]},unsigned,big]}], {x,2}}. {'%',{bin_opt,[17,{file,"t.erl"}]}}. {move,{x,0},{x,3}}. %% UNECESSARY! {test,is_ge,{f,3},[{x,2},{integer,127}]}. {line,[{location,"t.erl",18}]}. {gc_bif,'+',{f,0},4,[{x,1},{integer,1}],{x,1}}. {move,{x,3},{x,0}}. %% UNECESSARY! {call_only,2,{f,2}}. {label,3}. {line,[{location,"t.erl",20}]}. {gc_bif,'+',{f,0},4,[{x,1},{x,2}],{x,1}}. {move,{x,3},{x,0}}. %% UNECESSARY! {call_only,2,{f,2}}. {label,4}. {move,{x,1},{x,0}}. return. The redundant 'move' instructions have been marked. To avoid the 'move' instructions, we can extend the existing function is_context_unused/1 in v3_codegen. If v3_codegen can know that the match context will not be used again, it can reuse the register for the match context and avoid the extra 'move' instructions. https://bugs.erlang.org/browse/ERL-444
Diffstat (limited to 'bootstrap/lib')
0 files changed, 0 insertions, 0 deletions