Local linux builds should not enable PGO by default

[sbomer]

With recent upgrades to compiler versions (and upcoming upgrade to clang 16) in our official builds, our profile data uses an increasingly recent version of the PGO data format, which requires a similarly recent version of the compiler in order to optimize using this data.

Local builds and the runtime-dev-innerloop build should not enable PGO optimization in order to avoid requiring the very latest clang.

[ghost]

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Issue Details

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With recent upgrades to compiler versions (and upcoming upgrade to clang 16) in our official builds, our profile data uses an increasingly recent version of the PGO data format, which requires a similarly recent version of the compiler in order to optimize using this data.

Local builds and the runtime-dev-innerloop build should not enable PGO optimization in order to avoid requiring the very latest clang.

Author:	sbomer
Assignees:	-
Labels:	area-Infrastructure-coreclr, untriaged
Milestone:	-

[BruceForstall]

This is specifically about non-Windows builds, right? Presumably local Windows Release builds could continue to consume PGO data without issue?

[sbomer]

After some more thought, I think we should make this dependent on the compiler version. If your build machine has clang-16 available, there's no reason not to enable PGO. This makes the fix pretty simple, so I pushed it to #86436 to unblock the opt data flow. The fix will result in the following warning if clang-16 isn't available, but won't fail the build:

CMake Warning at pgosupport.cmake:79 (message):
    PGO is not supported; Clang 16 or later is required for profile guided
    optimizations

I initially stared going down the path of changing NoPgoOptimize to default to true for linux builds, and passing NoPgoOptimize=false where required. But I didn't like this for a few reasons:

• It requires passing more arguments through the already-complex yml.
• It makes it more difficult to repro ci builds locally (requires an extra argument, in addition to the latest compiler)
• NoPgoOptimize=false is just confusing (it doesn't mean PGO optimizations are enabled - only that PGO will be enabled in release builds, for supported platforms)

[sbomer]

Fixed in #86436.