[LV][EVL]Explicitly model AVL as sub, original TC, EVL_PHI.

Patch explicitly models AVL as sub original TC, EVL_PHI instead of
having it in EXPLICIT-VECTOR-LENGTH VPInstruction. Required for correct
safe dependence distance suport.

Reviewers: fhahn, ayalz

Reviewed By: ayalz

Pull Request: https://github.com/llvm/llvm-project/pull/108869

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -477,27 +477,19 @@ Value *VPInstruction::generate(VPTransformState &State) {
     return Builder.CreateSelect(Cmp, Sub, Zero);
   }
   case VPInstruction::ExplicitVectorLength: {
-    // Compute EVL
-    auto GetEVL = [=](VPTransformState &State, Value *AVL) {
-      assert(AVL->getType()->isIntegerTy() &&
-             "Requested vector length should be an integer.");
-
-      // TODO: Add support for MaxSafeDist for correct loop emission.
-      assert(State.VF.isScalable() && "Expected scalable vector factor.");
-      Value *VFArg = State.Builder.getInt32(State.VF.getKnownMinValue());
-
-      Value *EVL = State.Builder.CreateIntrinsic(
-          State.Builder.getInt32Ty(), Intrinsic::experimental_get_vector_length,
-          {AVL, VFArg, State.Builder.getTrue()});
-      return EVL;
-    };
     // TODO: Restructure this code with an explicit remainder loop, vsetvli can
     // be outside of the main loop.
-    // Compute VTC - IV as the AVL (requested vector length).
-    Value *Index = State.get(getOperand(0), VPIteration(0, 0));
-    Value *TripCount = State.get(getOperand(1), VPIteration(0, 0));
-    Value *AVL = State.Builder.CreateSub(TripCount, Index);
-    Value *EVL = GetEVL(State, AVL);
+    Value *AVL = State.get(getOperand(0), VPIteration(0, 0));
+    // Compute EVL
+    assert(AVL->getType()->isIntegerTy() &&
+           "Requested vector length should be an integer.");
+
+    assert(State.VF.isScalable() && "Expected scalable vector factor.");
+    Value *VFArg = State.Builder.getInt32(State.VF.getKnownMinValue());
+
+    Value *EVL = State.Builder.CreateIntrinsic(
+        State.Builder.getInt32Ty(), Intrinsic::experimental_get_vector_length,
+        {AVL, VFArg, State.Builder.getTrue()});
     return EVL;
   }
   case VPInstruction::CanonicalIVIncrementForPart: {

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -1423,7 +1423,8 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
 /// ...
 /// %EVLPhi = EXPLICIT-VECTOR-LENGTH-BASED-IV-PHI [ %StartV, %vector.ph ],
 ///                                               [ %NextEVLIV, %vector.body ]
-/// %VPEVL = EXPLICIT-VECTOR-LENGTH %EVLPhi, original TC
+/// %AVL = sub original TC, %EVLPhi
+/// %VPEVL = EXPLICIT-VECTOR-LENGTH %AVL
 /// ...
 /// %NextEVLIV = add IVSize (cast i32 %VPEVVL to IVSize), %EVLPhi
 /// ...
@@ -1453,9 +1454,15 @@ bool VPlanTransforms::tryAddExplicitVectorLength(VPlan &Plan) {
   // Create the ExplicitVectorLengthPhi recipe in the main loop.
   auto *EVLPhi = new VPEVLBasedIVPHIRecipe(StartV, DebugLoc());
   EVLPhi->insertAfter(CanonicalIVPHI);
-  auto *VPEVL = new VPInstruction(VPInstruction::ExplicitVectorLength,
-                                  {EVLPhi, Plan.getTripCount()});
-  VPEVL->insertBefore(*Header, Header->getFirstNonPhi());
+  // TODO: Add support for MaxSafeDist for correct loop emission.
+  // Compute original TC - IV as the AVL (application vector length).
+  auto *AVL = new VPInstruction(
+      Instruction::Sub, {Plan.getTripCount(), EVLPhi},
+      DebugLoc(), "avl");
+  AVL->insertBefore(*Header, Header->getFirstNonPhi());
+  auto *VPEVL =
+      new VPInstruction(VPInstruction::ExplicitVectorLength, AVL, DebugLoc());
+  VPEVL->insertAfter(AVL);
 
   auto *CanonicalIVIncrement =
       cast<VPInstruction>(CanonicalIVPHI->getBackedgeValue());

llvm/test/Transforms/LoopVectorize/RISCV/vplan-vp-intrinsics-reduction.ll

@@ -39,7 +39,8 @@ define i32 @reduction(ptr %a, i64 %n, i32 %start) {
 ; IF-EVL-INLOOP-NEXT:    EMIT vp<[[IV:%[0-9]+]]> = CANONICAL-INDUCTION
 ; IF-EVL-INLOOP-NEXT:    EXPLICIT-VECTOR-LENGTH-BASED-IV-PHI vp<[[EVL_PHI:%[0-9]+]]> = phi ir<0>, vp<[[IV_NEXT:%[0-9]+]]>
 ; IF-EVL-INLOOP-NEXT:    WIDEN-REDUCTION-PHI ir<[[RDX_PHI:%.+]]> = phi ir<%start>, ir<[[RDX_NEXT:%.+]]>
-; IF-EVL-INLOOP-NEXT:    EMIT vp<[[EVL:%.+]]> = EXPLICIT-VECTOR-LENGTH vp<[[EVL_PHI]]>, ir<%n>
+; IF-EVL-INLOOP-NEXT:    EMIT vp<[[AVL:%.+]]> = sub ir<%n>, vp<[[EVL_PHI]]>
+; IF-EVL-INLOOP-NEXT:    EMIT vp<[[EVL:%.+]]> = EXPLICIT-VECTOR-LENGTH vp<[[AVL]]>
 ; IF-EVL-INLOOP-NEXT:    vp<[[ST:%[0-9]+]]> = SCALAR-STEPS vp<[[EVL_PHI]]>, ir<1>
 ; IF-EVL-INLOOP-NEXT:    CLONE ir<[[GEP1:%.+]]> = getelementptr inbounds ir<%a>, vp<[[ST]]>
 ; IF-EVL-INLOOP-NEXT:    vp<[[PTR1:%[0-9]+]]> = vector-pointer ir<[[GEP1]]>

llvm/test/Transforms/LoopVectorize/RISCV/vplan-vp-intrinsics.ll

@@ -23,7 +23,8 @@ define void @foo(ptr noalias %a, ptr noalias %b, ptr noalias %c, i64 %N) {
 ; IF-EVL-NEXT:  vector.body:
 ; IF-EVL-NEXT:    EMIT vp<[[IV:%[0-9]+]]> = CANONICAL-INDUCTION
 ; IF-EVL-NEXT:    EXPLICIT-VECTOR-LENGTH-BASED-IV-PHI vp<[[EVL_PHI:%[0-9]+]]> = phi ir<0>, vp<[[IV_NEXT:%[0-9]+]]>
-; IF-EVL-NEXT:    EMIT vp<[[EVL:%.+]]> = EXPLICIT-VECTOR-LENGTH vp<[[EVL_PHI]]>, ir<%N>
+; IF-EVL-NEXT:    EMIT vp<[[AVL:%.+]]> = sub ir<%N>, vp<[[EVL_PHI]]>
+; IF-EVL-NEXT:    EMIT vp<[[EVL:%.+]]> = EXPLICIT-VECTOR-LENGTH vp<[[AVL]]>
 ; IF-EVL-NEXT:    vp<[[ST:%[0-9]+]]> = SCALAR-STEPS vp<[[EVL_PHI]]>, ir<1>
 ; IF-EVL-NEXT:    CLONE ir<[[GEP1:%.+]]> = getelementptr inbounds ir<%b>, vp<[[ST]]>
 ; IF-EVL-NEXT:    vp<[[PTR1:%[0-9]+]]> = vector-pointer ir<[[GEP1]]>