This commit fixes a regression (from LLVM 10 to LLVM 11 RC3) in the LLVM C API.
Previously, commit 1ee6ec2bf removed the mask operand from the
ShuffleVector instruction, storing the mask data separately in the instruction
instead; this reduced the number of operands of ShuffleVector from 3 to 2.
AFAICT, this change unintentionally caused a regression in the LLVM C API.
Specifically, it is no longer possible to get the mask of a ShuffleVector
instruction through the C API. This patch introduces new functions which
together allow a C API user to get the mask of a ShuffleVector instruction,
restoring the functionality which was previously available through
This patch also adds tests for this change to the llvm-c-test executable, which
involved adding support for InsertElement, ExtractElement, and ShuffleVector
itself (as well as constant vectors) to echo.cpp. Previously, vector
operations weren't tested at all in echo.ll.
I also fixed some typos in comments and help-text nearby these changes, which I
happened to spot while developing this patch. Since the typo fixes are technically
unrelated other than being in the same files, I'm happy to take them out if
you'd rather they not be included in the patch.
I'm not sure who the appropriate reviewer / code owner is for this diff,
so I'm taking a guess and adding @arsenm since they reviewed D67132 which
also touched the C API. If this is wrong, feel free to let me know.