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25168751
2009 Apr 20
1
[LLVMdev] How to prevent LLVM from undoing a custom lowering
My target has only logical shifts and lacks an arithmetic right shift
instruction.
I have a custom LowerSRA function that rewrites SRA as SHL + SIGN_EXTEND
when the shift width is either constant 16 or 24. Unfortunately, I
observe that a
later pass combines the SHL + SIGN_EXTEND back into SRA so we crash.
The idea I had for defeating this behavior is lower to a target-specific
version of SHL