[build_support] Added -sparse option for llvm-profdata if supported

[harlanhaskins]

What's in this pull request?

Adds the -sparse option to invocations of llvm-profdata if it's supported.
Abstracts out the lookup for llvm-profdata such that it can be replaced if/when #1586 is merged.

Resolved bug number: rdar://problem/25072811

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[harlanhaskins]

@vedantk

[vedantk]

Lgtm!

[harlanhaskins]

@gribozavr Mind taking a look? Thanks!

[harlanhaskins]

@vedantk Could you kindly ask @swift-ci to please test

[vedantk]

@harlanhaskins Does the 'please test' path invoke the profile merger?

[harlanhaskins]

Nope -- in fact, swift-ci doesn't have a command for that. So this won't be tested by CI...

[harlanhaskins]

I'm gonna write some tests for it.

[harlanhaskins]

Could I get a @swift-ci please python lint?

[vedantk]

@swift-ci Please python lint

[harlanhaskins]

Looks like that's just not gonna do anything right now. ¯_(ツ)_/¯

[shahmishal]

@swift-ci Please python lint

[harlanhaskins]

@shahmishal Shouldn't you be at home and not working? 😂

[shahmishal]

@swift-ci Please python lint

[shahmishal]

@harlanhaskins lol

[shahmishal]

@swift-ci Please python lint

[shahmishal]

@swift-ci Please python lint

[shahmishal]

--- Python lint ---
./utils/swift-api-dump.py:98:80: W291 trailing whitespace
./utils/swift-api-dump.py:99:80: E501 line too long (82 > 79 characters)

[shahmishal]

@swift-ci Please python lint

[shahmishal]

@harlanhaskins Thanks!

[harlanhaskins]

Good to merge?

[vedantk]

I lgtm'd this, but I think the code owner for utils/ should chime in. In particular, I'm not sure what the behavior of this script is on Linux. I see the FIXME saying non-Darwin platforms aren't supported, but it wouldn't be OK to, e.g crash on non-Darwin platforms. There's also the question of whether the import magic is standard (and I'm not the best person to answer that).

[harlanhaskins]

Once #1586 is merged, I can merge Linux support. Right now, non-Darwin is guarded inside main.py, but that will be removed once I can lookup llvm-profdata with host_toolchain()

[harlanhaskins]

@modocache @gribozavr Think this is good to merge?

[gribozavr]

Hardcoding the xcrun toolchain name is not correct in all cases, but should be a good start. LGTM otherwise.

[harlanhaskins]

Thanks!