[RISCV][CostModel] VPIntrinsics have same cost as their non-vp counterparts (#67178)

On RISCV, only a few VPIntrinsics have their cost modeled by the
VectorIntrinsicCostTable. Even so, none of those entries consider LMUL.
All other VPIntrinsics do not have meaningful modeling.

This patch models the cost of a VPIntrinsic as the cost of its non-VP
counterpart. It is possible that the VP Intrinsic is cheaper than the
non-VP
version depending on VL. On RISCV, this may be due two reasons (if the
instruction is part of a loop):
  1. A smaller VL can be used on the last iteration of the loop.
  2. The VP instruction may avoid a scalar remainder loop.

I have left this as a TODO since I think this change puts us on the
right path of modeling the cost of a VPInstruction, and it isn't
entirely clear to me how much of a discount we should give to a
known VL<VLMAX or what to do when VL is unknown at compile time.

Author: michaelmaitland

llvm/include/llvm/CodeGen/BasicTTIImpl.h

@@ -1686,6 +1686,62 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
     }
     }
 
+    // VP Intrinsics should have the same cost as their non-vp counterpart.
+    // TODO: Adjust the cost to make the vp intrinsic cheaper than its non-vp
+    // counterpart when the vector length argument is smaller than the maximum
+    // vector length.
+    if (VPIntrinsic::isVPIntrinsic(ICA.getID())) {
+      std::optional<unsigned> FOp =
+          VPIntrinsic::getFunctionalOpcodeForVP(ICA.getID());
+      if (FOp) {
+        // TODO: Support other kinds of Intrinsics (i.e. reductions)
+        if (ICA.getID() == Intrinsic::vp_load) {
+          Align Alignment;
+          if (auto *VPI = dyn_cast_or_null<VPIntrinsic>(ICA.getInst()))
+            Alignment = VPI->getPointerAlignment().valueOrOne();
+          unsigned AS = 0;
+          if (ICA.getArgs().size() > 1)
+            if (auto *PtrTy =
+                    dyn_cast<PointerType>(ICA.getArgs()[0]->getType()))
+              AS = PtrTy->getAddressSpace();
+          return thisT()->getMemoryOpCost(*FOp, ICA.getReturnType(), Alignment,
+                                          AS, CostKind);
+        }
+        if (ICA.getID() == Intrinsic::vp_store) {
+          Align Alignment;
+          if (auto *VPI = dyn_cast_or_null<VPIntrinsic>(ICA.getInst()))
+            Alignment = VPI->getPointerAlignment().valueOrOne();
+          unsigned AS = 0;
+          if (ICA.getArgs().size() >= 2)
+            if (auto *PtrTy =
+                    dyn_cast<PointerType>(ICA.getArgs()[1]->getType()))
+              AS = PtrTy->getAddressSpace();
+          return thisT()->getMemoryOpCost(*FOp, Args[0]->getType(), Alignment,
+                                          AS, CostKind);
+        }
+        if (VPBinOpIntrinsic::isVPBinOp(ICA.getID())) {
+          return thisT()->getArithmeticInstrCost(*FOp, ICA.getReturnType(),
+                                                 CostKind);
+        }
+      }
+
+      std::optional<Intrinsic::ID> FID =
+          VPIntrinsic::getFunctionalIntrinsicIDForVP(ICA.getID());
+      if (FID) {
+        // Non-vp version will have same Args/Tys except mask and vector length.
+        assert(ICA.getArgs().size() >= 2 && ICA.getArgTypes().size() >= 2 &&
+               "Expected VPIntrinsic to have Mask and Vector Length args and "
+               "types");
+        ArrayRef<const Value *> NewArgs = ArrayRef(ICA.getArgs()).drop_back(2);
+        ArrayRef<Type *> NewTys = ArrayRef(ICA.getArgTypes()).drop_back(2);
+
+        IntrinsicCostAttributes NewICA(*FID, ICA.getReturnType(), NewArgs,
+                                       NewTys, ICA.getFlags(), ICA.getInst(),
+                                       ICA.getScalarizationCost());
+        return thisT()->getIntrinsicInstrCost(NewICA, CostKind);
+      }
+    }
+
     // Assume that we need to scalarize this intrinsic.
     // Compute the scalarization overhead based on Args for a vector
     // intrinsic.

llvm/test/Analysis/CostModel/RISCV/gep.ll

@@ -270,7 +270,7 @@ define void @non_foldable_vector_uses(ptr %base, <2 x ptr> %base.vec) {
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %4 = getelementptr i8, ptr %base, i32 42
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 5 for instruction: %x4 = call <2 x i8> @llvm.masked.expandload.v2i8(ptr %4, <2 x i1> undef, <2 x i8> undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %5 = getelementptr i8, ptr %base, i32 42
-; RVI-NEXT:  Cost Model: Found an estimated cost of 5 for instruction: %x5 = call <2 x i8> @llvm.vp.load.v2i8.p0(ptr %5, <2 x i1> undef, i32 undef)
+; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %x5 = call <2 x i8> @llvm.vp.load.v2i8.p0(ptr %5, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %6 = getelementptr i8, ptr %base, i32 42
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 5 for instruction: %x6 = call <2 x i8> @llvm.experimental.vp.strided.load.v2i8.p0.i64(ptr %6, i64 undef, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %7 = getelementptr i8, ptr %base, i32 42
@@ -282,7 +282,7 @@ define void @non_foldable_vector_uses(ptr %base, <2 x ptr> %base.vec) {
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %10 = getelementptr i8, ptr %base, i32 42
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: call void @llvm.masked.compressstore.v2i8(<2 x i8> undef, ptr %10, <2 x i1> undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %11 = getelementptr i8, ptr %base, i32 42
-; RVI-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: call void @llvm.vp.store.v2i8.p0(<2 x i8> undef, ptr %11, <2 x i1> undef, i32 undef)
+; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: call void @llvm.vp.store.v2i8.p0(<2 x i8> undef, ptr %11, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %12 = getelementptr i8, ptr %base, i32 42
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: call void @llvm.experimental.vp.strided.store.v2i8.p0.i64(<2 x i8> undef, ptr %12, i64 undef, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
@@ -340,7 +340,7 @@ define void @foldable_vector_uses(ptr %base, <2 x ptr> %base.vec) {
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %4 = getelementptr i8, ptr %base, i32 0
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 5 for instruction: %x4 = call <2 x i8> @llvm.masked.expandload.v2i8(ptr %4, <2 x i1> undef, <2 x i8> undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %5 = getelementptr i8, ptr %base, i32 0
-; RVI-NEXT:  Cost Model: Found an estimated cost of 5 for instruction: %x5 = call <2 x i8> @llvm.vp.load.v2i8.p0(ptr %5, <2 x i1> undef, i32 undef)
+; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %x5 = call <2 x i8> @llvm.vp.load.v2i8.p0(ptr %5, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %6 = getelementptr i8, ptr %base, i32 0
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 5 for instruction: %x6 = call <2 x i8> @llvm.experimental.vp.strided.load.v2i8.p0.i64(ptr %6, i64 undef, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %7 = getelementptr i8, ptr %base, i32 0
@@ -352,7 +352,7 @@ define void @foldable_vector_uses(ptr %base, <2 x ptr> %base.vec) {
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %10 = getelementptr i8, ptr %base, i32 0
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: call void @llvm.masked.compressstore.v2i8(<2 x i8> undef, ptr %10, <2 x i1> undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %11 = getelementptr i8, ptr %base, i32 0
-; RVI-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: call void @llvm.vp.store.v2i8.p0(<2 x i8> undef, ptr %11, <2 x i1> undef, i32 undef)
+; RVI-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: call void @llvm.vp.store.v2i8.p0(<2 x i8> undef, ptr %11, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %12 = getelementptr i8, ptr %base, i32 0
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: call void @llvm.experimental.vp.strided.store.v2i8.p0.i64(<2 x i8> undef, ptr %12, i64 undef, <2 x i1> undef, i32 undef)
 ; RVI-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void