search for: volatile_copy

...) The value read from a reserved register cannot be predicted. Reading a reserved register twice may each time produce a different result. This seems broken to me that treating another copy should be assumed to produce a different result. This seems like it should be optimized, and have a special volatile_copy instruction for the special cases where the reserved register may randomly change. -Matt

...he value read from a reserved register cannot be predicted. Reading a reserved register twice may each time produce a different result. > This seems broken to me that treating another copy should be assumed to produce a different result. This seems like it should be optimized, and have a special volatile_copy instruction for the special cases where the reserved register may randomly change. > > -Matt > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

...alue read from a reserved register cannot be predicted. Reading a reserved register twice may each time produce a different result. >> This seems broken to me that treating another copy should be assumed to produce a different result. This seems like it should be optimized, and have a special volatile_copy instruction for the special cases where the reserved register may randomly change. >> >> -Matt >> _______________________________________________ >> LLVM Developers mailing list >> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> >> http://li...

Lately I have had a few discussions of what it means for a register to be unallocatable or reserved. As this comes up every now and again and I often struggled answering such questions I decided to write down some definite rules and codify the current usage and assumptions. I plan to put the rules below into the doxygen comments of MachineRegisterInfo etc. And I also hope that people will correct