This patch teaches llvm-mca how to parse code comments in search for special "markers" used to select regions of code.
# LLVM-MCA-START My Code Region .... # LLVM-MCA-END
The MCAsmLexer now delegates to an object of class MCACommentParser (i.e. an AsmCommentConsumer) the parsing of code comments to search for begin/end code region markers.
A comment starting with substring "LLVM-MCA-START" marks the beginning of a new region of code.
A comment starting with substring "LLVM-MCA-END" marks the end of the last region.
This implementation doesn't allow regions to overlap. Each region can have a optional description; internally, each region is described by a range of source code locations (SMLoc).
MCInst objects are added to a region R only if the source location for the MCInst is in the range of locations specified by R.
By default, the tool allocates an implicit "Default" code region which contains every source location.
See new tests llvm-mca-marker-*.s for a few examples.
How this affect the report generated by the tool?
A new Backend object is created for every region. So, the analysis is conducted on every parsed code region.
The final report is the union of the reports generated for every code region. Note that empty regions are skipped.
Special "[#] Code Region - ..." strings are used in the report to mark the portion which is specific to a code region only. For example, see llvm-mca-markers-5.s.
Please let me know if okay to commit.