[llvm] [VPlan] Add hidden `-vplan-print-after-all` option (PR #175839)

[Luke Lau via llvm-commits]

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@@ -933,7 +936,12 @@ void VPlan::execute(VPTransformState *State) {
   LLVM_DEBUG(dbgs() << "Executing best plan with VF=" << State->VF
                     << ", UF=" << getUF() << '\n');
   setName("Final VPlan");
+  // TODO: -debug-only=loop-vectorize should probably just imply
+  // `-vplan-print-after-all`, but the latter is much more verbose than the
+  // former, so doing that would require updating existing tests and that hasn't
+  // been done (yet). For now, just do both:
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lukel97 wrote:

I'm not sure if -debug-only=loop-vectorize should imply -vplan-print-after-all given we use it for VPlan tests, I'd imagine that might cause issues with CHECK lines. I presume all the intermediate VPlans have the same "initial vplan" name?

Given that I'd be happy with just having the existing "final vplan" dump from the debug output. 

https://github.com/llvm/llvm-project/pull/175839