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authorBjörn Gustavsson <[email protected]>2016-06-02 09:58:46 +0200
committerBjörn Gustavsson <[email protected]>2016-06-02 12:51:18 +0200
commit5facb518a9ee2d756564eccd92a2c11f334d6282 (patch)
tree459b4574356863255a4e27aa017c04796780fdd9 /lib/jinterface/.gitignore
parentaab1db16d0a732823fa9e2964c6a52b109c61742 (diff)
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Eliminate crash for map updates in guards
beam_validator would complain that x(1) is uninitialized in a test_heap instruction when attempting to compile the following code with sys_core_fold turned off: foo(M) when not (M#{true := 0}); [M] -> ok. Simplified, the generated BEAM assembly code looked like this: test is_map BadMap x(0) put_map_exact Fail x(0) => x(1) ... jump BooleanStuff BadMap: move ok => x(1) jump Fail BooleanStuff: ... move Boolean => x(2) jump Build Fail: move false => x(2) Build: test_heap 2 3 %% x(0), x(1), x(2) must be live. ... That is, if put_map_exact failed, control would transfer to the label Fail without initializing x(1). Fix that by making sure that x(1) is initilized even if put_map_exact fails: test is_map BadMap x(0) put_map_exact BadLbl x(0) => x(1) ... jump OkLbl BadLbl: move ok => x(1) jump Fail OkLbl: jump BooleanStuff BadMap: move ok => x(1) jump Fail BooleanStuff: ... move Boolean => x(2) jump Build Fail: move false => x(2) Build: test_heap 2 3 %% x(0), x(1), x(2) must be live. ... Note that this situation is rare, and that other optimization passes (beam_dead and beam_jump in particular) will clean up this mess.
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