[CodeGen][PM] Use errs() instead of dbgs() in printer passes

[optimisan]

Use the buffered stream for printing analysis info in the pipeline.

[optimisan]

• [CodeGen][PM] Use errs() instead of dbgs() in printer passes #118469 👈 (View in Graphite)
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[paperchalice]

In fact I see llvm::errs() is also unbuffered:

llvm-project/llvm/lib/Support/raw_ostream.cpp

Lines 910 to 915 in 81d82ca

	// Set standard error to be unbuffered.
	#ifdef __MVS__
	std::error_code EC = enablezOSAutoConversion(STDERR_FILENO);
	assert(!EC);
	#endif
	static raw_fd_ostream S(STDERR_FILENO, false, true);

But +1 for this, because dbg() should be used in debug context and is no different with errs() in release build.