[VPlan] Also check if plan for best legacy VF contains simplifications.

The plan for the VF chosen by the legacy cost model could also contain
additional simplifications that cause cost differences. Also check if it
contains simplifications.

Fixes #114860.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7521,6 +7521,8 @@ VectorizationFactor LoopVectorizationPlanner::computeBestVF() {
   precomputeCosts(BestPlan, BestFactor.Width, CostCtx);
   assert((BestFactor.Width == LegacyVF.Width ||
           planContainsAdditionalSimplifications(getPlanFor(BestFactor.Width),
+                                                CostCtx, OrigLoop) ||
+          planContainsAdditionalSimplifications(getPlanFor(LegacyVF.Width),
                                                 CostCtx, OrigLoop)) &&
          " VPlan cost model and legacy cost model disagreed");
   assert((BestFactor.Width.isScalar() || BestFactor.ScalarCost > 0) &&

llvm/test/Transforms/LoopVectorize/RISCV/select-invariant-cond-cost.ll

@@ -0,0 +1,49 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -p loop-vectorize -S %s | FileCheck %s
+
+target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
+target triple = "riscv64-unknown-linux-gnu"
+
+; Test for https://github.com/llvm/llvm-project/issues/114860.
+define void @test_invariant_cond_for_select(ptr %dst, i8 %x) #0 {
+; CHECK-LABEL: define void @test_invariant_cond_for_select(
+; CHECK-SAME: ptr [[DST:%.*]], i8 [[X:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[C_1:%.*]] = icmp eq i8 [[X]], 0
+; CHECK-NEXT:    [[C_2:%.*]] = icmp sgt i64 [[IV]], 0
+; CHECK-NEXT:    [[C_2_EXT:%.*]] = zext i1 [[C_2]] to i64
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[C_1]], i64 [[C_2_EXT]], i64 0
+; CHECK-NEXT:    [[SEL_TRUNC:%.*]] = trunc i64 [[SEL]] to i8
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[DST]], i64 [[IV]]
+; CHECK-NEXT:    store i8 [[SEL_TRUNC]], ptr [[GEP]], align 1
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 4
+; CHECK-NEXT:    [[EC:%.*]] = icmp ult i64 [[IV]], 14
+; CHECK-NEXT:    br i1 [[EC]], label %[[LOOP]], label %[[EXIT:.*]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %c.1 = icmp eq i8 %x, 0
+  %c.2 = icmp sgt i64 %iv, 0
+  %c.2.ext = zext i1 %c.2 to i64
+  %sel = select i1 %c.1, i64 %c.2.ext, i64 0
+  %sel.trunc = trunc i64 %sel to i8
+  %gep = getelementptr inbounds i8, ptr %dst, i64 %iv
+  store i8 %sel.trunc, ptr %gep, align 1
+  %iv.next = add i64 %iv, 4
+  %ec = icmp ult i64 %iv, 14
+  br i1 %ec, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+attributes #0 = { "target-features"="+64bit,+v" }
+