No basic block terminator in a fall-thru #14
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ksolana
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Apr 1, 2024
| let terminator = LLVMGetBasicBlockTerminator(prev_bb); | ||
| if terminator.is_null() { | ||
| LLVMPositionBuilderAtEnd(self.module_cx.llvm_builder.0, prev_bb); | ||
| LLVMBuildBr(self.module_cx.llvm_builder.0, bb); |
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How do we know that LLVMGetPreviousBasicBlock gives a predecessor of bb? Even if this somehow works, this can lead to bug in future.
I think we should keep track of previous basic block in translate_instruction and pass that information to fix_terminator_in_prev_bb
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Yes, we know that LLVMGetPreviousBasicBlock gives the correct predecessor since it is how we build them in translate_instruction.
Providing an additional tracking will be just an unnecessary double booking.
ksolana
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Apr 1, 2024
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@ksolana thx for quick review! |
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Thanks @jcivlin |
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Jun 14, 2024
* 032424-failure-loop: ini * 032424-failure-loop: fix_bb_terminator * 032424-failure-loop: fix in sbc::Bytecode::Label * 032424-failure-loop: add failure-tests * 032424-failure-loop: fix_bb_terminators and fix_terminator_in_prev_bb
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Problem description
Stackless code may have basic block terminators removed by Move compiler optimizer (which is semantically ok for the fall-thru), whereas LLVM requires terminators in all basic blocks (even for the fall-thru).
Solution
This patch provides fixing of this problem and adds (restores) the omitted basic block terminator while translating
sbc::Bytecode::Label bytecode.
Example
For this test:
In the generated code the first br was absent and added in this patch: