[VPlan] Handle conditional ordered reductions with scalar VFs.

VPReductionRecipe::execute was not handling predicates for ordered
reduction with scalar VFs, which was causing a crash. Thsi patch adds
dedicated handling for scalar VFs when dealing with the condition.
The other operands are already handled in a similar fashion below.

Fixes #70988.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -9399,12 +9399,16 @@ void VPReductionRecipe::execute(VPTransformState &State) {
     Value *NewVecOp = State.get(getVecOp(), Part);
     if (VPValue *Cond = getCondOp()) {
       Value *NewCond = State.get(Cond, Part);
-      VectorType *VecTy = cast<VectorType>(NewVecOp->getType());
-      Value *Iden = RdxDesc.getRecurrenceIdentity(Kind, VecTy->getElementType(),
+      VectorType *VecTy = dyn_cast<VectorType>(NewVecOp->getType());
+      Type *ElementTy = VecTy ? VecTy->getElementType() : NewVecOp->getType();
+      Value *Iden = RdxDesc.getRecurrenceIdentity(Kind, ElementTy,
                                                   RdxDesc.getFastMathFlags());
-      Value *IdenVec =
-          State.Builder.CreateVectorSplat(VecTy->getElementCount(), Iden);
-      Value *Select = State.Builder.CreateSelect(NewCond, NewVecOp, IdenVec);
+      if (State.VF.isVector()) {
+        Iden =
+            State.Builder.CreateVectorSplat(VecTy->getElementCount(), Iden);
+      }
+
+      Value *Select = State.Builder.CreateSelect(NewCond, NewVecOp, Iden);
       NewVecOp = Select;
     }
     Value *NewRed;

llvm/test/Transforms/LoopVectorize/strict-fadd-interleave-only.ll

@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -passes=loop-vectorize -prefer-predicate-over-epilogue=predicate-else-scalar-epilogue -force-vector-interleave=2 -force-vector-width=1 -force-ordered-reductions -S %s | FileCheck %s
+
+define float @pr70988() {
+; CHECK-LABEL: define float @pr70988() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX1:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT3:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi float [ 0.000000e+00, [[VECTOR_PH]] ], [ [[TMP5:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IV:%.*]] = add i32 [[INDEX1]], 0
+; CHECK-NEXT:    [[VEC_IV2:%.*]] = add i32 [[INDEX1]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ule i32 [[VEC_IV]], 1020
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ule i32 [[VEC_IV2]], 1020
+; CHECK-NEXT:    [[TMP2:%.*]] = select contract i1 [[TMP0]], float 1.000000e+00, float -0.000000e+00
+; CHECK-NEXT:    [[TMP3:%.*]] = fadd contract float [[VEC_PHI]], [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = select contract i1 [[TMP1]], float 1.000000e+00, float -0.000000e+00
+; CHECK-NEXT:    [[TMP5]] = fadd contract float [[TMP3]], [[TMP4]]
+; CHECK-NEXT:    [[INDEX_NEXT3]] = add i32 [[INDEX1]], 2
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[INDEX_NEXT3]], 1022
+; CHECK-NEXT:    br i1 [[TMP6]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    br i1 true, label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ 1022, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi float [ 0.000000e+00, [[ENTRY]] ], [ [[TMP5]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INDEX_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[RDX:%.*]] = phi float [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[RDX_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[RDX_NEXT]] = fadd contract float [[RDX]], 1.000000e+00
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw nsw i32 [[INDEX]], 1
+; CHECK-NEXT:    [[COND:%.*]] = icmp ult i32 [[INDEX_NEXT]], 1021
+; CHECK-NEXT:    br i1 [[COND]], label [[LOOP]], label [[EXIT]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi float [ [[RDX_NEXT]], [[LOOP]] ], [ [[TMP5]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    ret float [[DOTLCSSA]]
+;
+entry:
+  br label %loop
+
+loop:
+  %index = phi i32 [ 0, %entry ], [ %index.next, %loop ]
+  %rdx = phi float [ 0.000000e+00, %entry ], [ %rdx.next, %loop ]
+  %rdx.next = fadd contract float %rdx, 1.000000e+00
+  %index.next = add nuw nsw i32 %index, 1
+  %cond = icmp ult i32 %index.next, 1021
+  br i1 %cond, label %loop, label %exit
+
+exit:
+  %.lcssa = phi float [ %rdx.next, %loop ]
+  ret float %.lcssa
+}