[llvm] [VPlan] Preserve branch weights from VPlan0 through to codegen. (PR #213143)

[Florian Hahn via llvm-commits]

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@@ -483,6 +483,14 @@ static bool mergeReplicateRegionsIntoSuccessors(VPlan &Plan) {
     if (!Then1 || !Then2)
       continue;
 
+    // The merged region is entered whenever either of the original regions was,
+    // so use the higher, i.e. more conservative, of their entry probabilities.
+    VPBranchOnMaskRecipe *Guard2 = Region2->getEntryBranchOnMask();
+    VPExecutionProbability Prob1 =
+        Region1->getEntryBranchOnMask()->getExecutionProbability();
+    if (!Prob1.isUnknown() && Guard2->getExecutionProbability() < Prob1)
+      Guard2->setExecutionProbability(Prob1, Plan.getContext());
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fhahn wrote:

Added, but I couldn't get it to crash, II think this is handled by `<`.

https://github.com/llvm/llvm-project/pull/213143