JIT: Don't run optSetBlockWeights when we have PGO data

[amanasifkhalid]

Part of #107749. For PGO scenarios, we plan to rely entirely on profile synthesis to propagate profile-derived weights throughout the flowgraph. This is the first step in transitioning away from the existing weight propagation heuristics. We want to keep these around for non-PGO scenarios for now, though ideally, we'll eventually be able to replace these entirely with profile synthesis (plus branch prediction heuristics when we don't have profile data), and consolidate how the profile is maintained for PGO and non-PGO scenarios.

This had few diffs locally, as optSetBlockWeights already avoids modifying profile-derived weights. The diffs seem to stem from BBF_PROF_WEIGHT not being propagated to all blocks when we have profile data (such as during inlining). This doesn't seem concerning, since the next profile repair pass (which I've yet to add) will propagate the flag as needed.

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[AndyAyersMS]

The diffs seem to stem from BBF_PROF_WEIGHT not being propagated to all blocks when we have profile data (such as during inlining). This doesn't seem concerning, since the next profile repair pass (which I've yet to add) will propagate the flag as needed.

I would rather see us strive to get these flags set properly by each phase that manipulates flow. So yet another aspect of pgo post phase checks: if root method has PGO, all blocks must have BBF_PROF_WEIGHT

[amanasifkhalid]

I would rather see us strive to get these flags set properly by each phase that manipulates flow. So yet another aspect of pgo post phase checks: if root method has PGO, all blocks must have BBF_PROF_WEIGHT

That sounds like a better plan. I suppose a reasonable goal is to enable BBF_PROF_WEIGHT propagation up to optSetBlockWeights to make this PR zero-diff, then get this checked in (while progressing the flag checks in tandem)?

[amanasifkhalid]

Diffs are smaller this time around; some of these are probably from the bbNum dependency we still have in fgUpdateFlowGraph, since we're skipping block renumbering when we have PGO data.