[LV] Check isPredInst instead of isScalarWithPred in uniform analysis. (#98892)

Any instruction marked as uniform will result in a uniform
VPReplicateRecipe. If it requires predication, it will be placed in a
replicate region, even if isScalarWithPredication returns false.

Check isPredicatedInst instead of isScalarWithPredication to avoid
generating uniform VPReplicateRecipes placed inside a replicate region.
This fixes an assertion when using scalable VFs.

Fixes #80416. 
Fixes #94328.
Fixes #99625.

PR: #98892

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3914,19 +3914,19 @@ void LoopVectorizationCostModel::collectLoopUniforms(ElementCount VF) {
   SetVector<Instruction *> Worklist;
 
   // Add uniform instructions demanding lane 0 to the worklist. Instructions
-  // that are scalar with predication must not be considered uniform after
+  // that require predication must not be considered uniform after
   // vectorization, because that would create an erroneous replicating region
   // where only a single instance out of VF should be formed.
-  // TODO: optimize such seldom cases if found important, see PR40816.
   auto addToWorklistIfAllowed = [&](Instruction *I) -> void {
     if (isOutOfScope(I)) {
       LLVM_DEBUG(dbgs() << "LV: Found not uniform due to scope: "
                         << *I << "\n");
       return;
     }
-    if (isScalarWithPredication(I, VF)) {
-      LLVM_DEBUG(dbgs() << "LV: Found not uniform being ScalarWithPredication: "
-                        << *I << "\n");
+    if (isPredicatedInst(I)) {
+      LLVM_DEBUG(
+          dbgs() << "LV: Found not uniform due to requiring predication: " << *I
+                 << "\n");
       return;
     }
     LLVM_DEBUG(dbgs() << "LV: Found uniform instruction: " << *I << "\n");
@@ -9516,6 +9516,8 @@ void VPInterleaveRecipe::execute(VPTransformState &State) {
 void VPReplicateRecipe::execute(VPTransformState &State) {
   Instruction *UI = getUnderlyingInstr();
   if (State.Instance) { // Generate a single instance.
+    assert((State.VF.isScalar() || !isUniform()) &&
+           "uniform recipe shouldn't be predicated");
     assert(!State.VF.isScalable() && "Can't scalarize a scalable vector");
     State.ILV->scalarizeInstruction(UI, this, *State.Instance, State);
     // Insert scalar instance packing it into a vector.