Change

Adds a new Triple::str(N) method, which returns the triple string but only keep the first N components. See method doc for details.

Note that the return type is StringRef. This is different from the existing methods, where const std::string & is returned by Triple::str() and Triple::getTriple(). The reason for StringRef is performance - it's unnecessary to create a new std::string object, which would copy the content of the triple string.

Usage

This method can remove trailing components (e.g. "object format") for edit or display purposes.

Alternatives

Alternative 1: Add the same method but return std::string for slightly more consistency with the existing methods. However, we probably don't want to make unnecessary copies just to make the API look more consistent. Also, it wouldn't be completely the same, because one is std::string and the other is const std::string &.

Alternative 2: Add a new method called Triple::clone(N = 5), which will return a new triple with the triple string that would be returned by Triple::str(N). However, the user might not want to construct a new triple object, or maybe they want to normalize it before creating such object. Triple::str(N) is more flexible.

Tests

Added TripleTest::StrFirstN.

$ ninja llvm-test-depends
$ unittests/TargetParser/TargetParserTests --gtest_filter="*StrFirstN*"
...
[ RUN      ] TripleTest.StrFirstN
[       OK ] TripleTest.StrFirstN (0 ms)