[llvm] [VPlan] Preserve the branch weights of scalarized selects. (PR #224968)

[David Sherwood via llvm-commits]

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@@ -527,6 +527,13 @@ void VPlanTransforms::convertToConcreteRecipes(VPlan &Plan) {
            vp_depth_first_deep(Plan.getEntry()))) {
     for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
       VPBuilder Builder(&R);
+      // !prof is only supported on scalar selects.
+      if (auto *Widen = dyn_cast<VPWidenRecipe>(&R)) {
+        if (Widen->getOpcode() == Instruction::Select &&
+            !vputils::isSingleScalar(Widen->getOperand(0)))
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david-arm wrote:

Is it worth adding a TODO here to add support for vector conditions too? If the select is going to be scalarised, then each lane of the condition will become scalar and hence we can also support branch weights.

https://github.com/llvm/llvm-project/pull/224968