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addc
2011 Nov 09
1
[LLVMdev] Inserting stack spilling code that modifies globally visible state
...odifies the machine FLAGS register (i.e. globally
visible state). The LLVM core code does not know about this 'feature'
and happily inserts spilling code anywhere it wants, thus
(potentially) corrupting live FLAGS.
Practically, the FLAGS register is used only for multi-byte arithmetic
(ADD+ADDCY pair), and conditional jumps (COMPARE+JUMP pair). Thus the
FLAGS register live-range, which is correctly (I hope) expressed in
the IR and it is visible to the reg. allocator and to all the existing
machinery, is usually very short. All I need is that the spilling code
would be never inserted into a...