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authorBjörn Gustavsson <[email protected]>2016-08-01 17:06:40 +0200
committerBjörn Gustavsson <[email protected]>2016-08-05 10:58:12 +0200
commit921cf991e09698d63d0f4f9a20bf2cfc23b2e896 (patch)
tree7513a85a22254cedc97bf95d4fdb64a61166cf53 /bootstrap/lib/kernel/ebin/global.beam
parent6dcf9c56c648bb6fa2f0e27bdf6429eab23fdd8c (diff)
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beam_block: Fix potentially unsafe optimization in move_allocates/1
beam_block has an optimization that only is safe when it is applied immediately after code generation. That is pointed out in a comment: NOTE: Moving allocation instructions is only safe because it is done immediately after code generation so that we KNOW that if {x,X} is initialized, all x registers with lower numbers are also initialized. That assumption may not be true after other optimizations, such as the beam_utils:live_opt/1 optimization. The new beam_reorder pass added in OTP 19 runs before beam_block. Therefore, the optimization is potentially unsafe. The optimization is also unsafe if compilation is started from assembly code in a .S file. Rewrite the optimization to make it safe. See the newly added comment for details. ERL-202
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