[IVDescriptors] Add pointer InductionDescriptors with non-constant strides

This matches the handling for integer IVs.  I left the non-opaque cases alone, mostly because they're largely irrelevant today.

This doesn't actually make much difference in vectorization right now as we immediately fail on aliasing checks (which also bail on non-constant strides).  Slightly suprisingly, it's the case which *do* need runtime checks which work after this patch as they don't use the same dependency analysis path.

This will also enable non-constant stride pointer recurrences for other consumers.  I've auditted said code, and don't see any obvious issues.

Author: preames

llvm/lib/Analysis/IVDescriptors.cpp

@@ -1288,8 +1288,6 @@ InductionDescriptor::InductionDescriptor(Value *Start, InductionKind K,
   assert((!getConstIntStepValue() || !getConstIntStepValue()->isZero()) &&
          "Step value is zero");
 
-  assert((IK != IK_PtrInduction || getConstIntStepValue()) &&
-         "Step value should be constant for pointer induction");
   assert((IK == IK_FpInduction || Step->getType()->isIntegerTy()) &&
          "StepValue is not an integer");
 
@@ -1570,15 +1568,25 @@ bool InductionDescriptor::isInductionPHI(
   }
 
   assert(PhiTy->isPointerTy() && "The PHI must be a pointer");
+  PointerType *PtrTy = cast<PointerType>(PhiTy);
+
+  // Always use i8 element type for opaque pointer inductions.
+  // This allows induction variables w/non-constant steps.
+  if (PtrTy->isOpaque()) {
+    D = InductionDescriptor(StartValue, IK_PtrInduction, Step,
+                            /* BinOp */ nullptr,
+                            Type::getInt8Ty(PtrTy->getContext()));
+    return true;
+  }
+
   // Pointer induction should be a constant.
+  // TODO: This could be generalized, but should probably just
+  // be dropped instead once the migration to opaque ptrs is
+  // complete.
   if (!ConstStep)
     return false;
 
-  // Always use i8 element type for opaque pointer inductions.
-  PointerType *PtrTy = cast<PointerType>(PhiTy);
-  Type *ElementType = PtrTy->isOpaque()
-                          ? Type::getInt8Ty(PtrTy->getContext())
-                          : PtrTy->getNonOpaquePointerElementType();
+  Type *ElementType = PtrTy->getNonOpaquePointerElementType();
   if (!ElementType->isSized())
     return false;
 

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2492,8 +2492,6 @@ static Value *emitTransformedIndex(IRBuilderBase &B, Value *Index,
     return CreateAdd(StartValue, Offset);
   }
   case InductionDescriptor::IK_PtrInduction: {
-    assert(isa<Constant>(Step) &&
-           "Expected constant step for pointer induction");
     return B.CreateGEP(ID.getElementType(), StartValue, CreateMul(Index, Step));
   }
   case InductionDescriptor::IK_FpInduction: {
@@ -8271,7 +8269,6 @@ VPRecipeBase *VPRecipeBuilder::tryToOptimizeInductionPHI(
   if (auto *II = Legal->getPointerInductionDescriptor(Phi)) {
     VPValue *Step = vputils::getOrCreateVPValueForSCEVExpr(Plan, II->getStep(),
                                                            *PSE.getSE());
-    assert(isa<SCEVConstant>(II->getStep()));
     return new VPWidenPointerInductionRecipe(
         Phi, Operands[0], Step, *II,
         LoopVectorizationPlanner::getDecisionAndClampRange(
@@ -9377,8 +9374,6 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
     return;
   }
 
-  assert(isa<SCEVConstant>(IndDesc.getStep()) &&
-         "Induction step not a SCEV constant!");
   Type *PhiType = IndDesc.getStep()->getType();
 
   // Build a pointer phi

llvm/test/Transforms/LoopVectorize/RISCV/strided-accesses.ll

@@ -539,19 +539,89 @@ exit:
 define void @double_stride_ptr_iv(ptr %p, ptr %p2, i64 %stride) {
 ; CHECK-LABEL: @double_stride_ptr_iv(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP1:%.*]] = mul i64 [[TMP0]], 4
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.umax.i64(i64 8, i64 [[TMP1]])
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 1024, [[TMP2]]
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_SCEVCHECK:%.*]]
+; CHECK:       vector.scevcheck:
+; CHECK-NEXT:    [[IDENT_CHECK:%.*]] = icmp ne i64 [[STRIDE:%.*]], 1
+; CHECK-NEXT:    br i1 [[IDENT_CHECK]], label [[SCALAR_PH]], label [[VECTOR_MEMCHECK:%.*]]
+; CHECK:       vector.memcheck:
+; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, ptr [[P2:%.*]], i64 1027
+; CHECK-NEXT:    [[SCEVGEP1:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 1027
+; CHECK-NEXT:    [[BOUND0:%.*]] = icmp ult ptr [[P2]], [[SCEVGEP1]]
+; CHECK-NEXT:    [[BOUND1:%.*]] = icmp ult ptr [[P]], [[SCEVGEP]]
+; CHECK-NEXT:    [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
+; CHECK-NEXT:    br i1 [[FOUND_CONFLICT]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[TMP3:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP4:%.*]] = mul i64 [[TMP3]], 4
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 1024, [[TMP4]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 1024, [[N_MOD_VF]]
+; CHECK-NEXT:    [[TMP5:%.*]] = mul i64 [[N_VEC]], [[STRIDE]]
+; CHECK-NEXT:    [[IND_END:%.*]] = getelementptr i8, ptr [[P]], i64 [[TMP5]]
+; CHECK-NEXT:    [[TMP6:%.*]] = mul i64 [[N_VEC]], [[STRIDE]]
+; CHECK-NEXT:    [[IND_END3:%.*]] = getelementptr i8, ptr [[P2]], i64 [[TMP6]]
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[POINTER_PHI:%.*]] = phi ptr [ [[P]], [[VECTOR_PH]] ], [ [[PTR_IND:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[POINTER_PHI7:%.*]] = phi ptr [ [[P2]], [[VECTOR_PH]] ], [ [[PTR_IND8:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP7:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP8:%.*]] = mul i64 [[TMP7]], 4
+; CHECK-NEXT:    [[TMP9:%.*]] = mul i64 [[TMP8]], 1
+; CHECK-NEXT:    [[TMP10:%.*]] = mul i64 [[STRIDE]], [[TMP9]]
+; CHECK-NEXT:    [[TMP11:%.*]] = mul i64 [[TMP8]], 0
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[TMP11]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <vscale x 4 x i64> [[DOTSPLATINSERT]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP12:%.*]] = call <vscale x 4 x i64> @llvm.experimental.stepvector.nxv4i64()
+; CHECK-NEXT:    [[TMP13:%.*]] = add <vscale x 4 x i64> [[DOTSPLAT]], [[TMP12]]
+; CHECK-NEXT:    [[DOTSPLATINSERT5:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[STRIDE]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT6:%.*]] = shufflevector <vscale x 4 x i64> [[DOTSPLATINSERT5]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[VECTOR_GEP:%.*]] = mul <vscale x 4 x i64> [[TMP13]], [[DOTSPLAT6]]
+; CHECK-NEXT:    [[TMP14:%.*]] = getelementptr i8, ptr [[POINTER_PHI]], <vscale x 4 x i64> [[VECTOR_GEP]]
+; CHECK-NEXT:    [[TMP15:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP16:%.*]] = mul i64 [[TMP15]], 4
+; CHECK-NEXT:    [[TMP17:%.*]] = mul i64 [[TMP16]], 1
+; CHECK-NEXT:    [[TMP18:%.*]] = mul i64 [[STRIDE]], [[TMP17]]
+; CHECK-NEXT:    [[TMP19:%.*]] = mul i64 [[TMP16]], 0
+; CHECK-NEXT:    [[DOTSPLATINSERT9:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[TMP19]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT10:%.*]] = shufflevector <vscale x 4 x i64> [[DOTSPLATINSERT9]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP20:%.*]] = call <vscale x 4 x i64> @llvm.experimental.stepvector.nxv4i64()
+; CHECK-NEXT:    [[TMP21:%.*]] = add <vscale x 4 x i64> [[DOTSPLAT10]], [[TMP20]]
+; CHECK-NEXT:    [[VECTOR_GEP13:%.*]] = mul <vscale x 4 x i64> [[TMP21]], [[DOTSPLAT6]]
+; CHECK-NEXT:    [[TMP22:%.*]] = getelementptr i8, ptr [[POINTER_PHI7]], <vscale x 4 x i64> [[VECTOR_GEP13]]
+; CHECK-NEXT:    [[WIDE_MASKED_GATHER:%.*]] = call <vscale x 4 x i32> @llvm.masked.gather.nxv4i32.nxv4p0(<vscale x 4 x ptr> [[TMP14]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer), <vscale x 4 x i32> poison), !alias.scope !16
+; CHECK-NEXT:    [[TMP23:%.*]] = add <vscale x 4 x i32> [[WIDE_MASKED_GATHER]], shufflevector (<vscale x 4 x i32> insertelement (<vscale x 4 x i32> poison, i32 1, i64 0), <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    call void @llvm.masked.scatter.nxv4i32.nxv4p0(<vscale x 4 x i32> [[TMP23]], <vscale x 4 x ptr> [[TMP22]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer)), !alias.scope !19, !noalias !16
+; CHECK-NEXT:    [[TMP24:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP25:%.*]] = mul i64 [[TMP24]], 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP25]]
+; CHECK-NEXT:    [[PTR_IND]] = getelementptr i8, ptr [[POINTER_PHI]], i64 [[TMP10]]
+; CHECK-NEXT:    [[PTR_IND8]] = getelementptr i8, ptr [[POINTER_PHI7]], i64 [[TMP18]]
+; CHECK-NEXT:    [[TMP26:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP26]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP21:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1024, [[N_VEC]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ], [ 0, [[VECTOR_SCEVCHECK]] ], [ 0, [[VECTOR_MEMCHECK]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL2:%.*]] = phi ptr [ [[IND_END]], [[MIDDLE_BLOCK]] ], [ [[P]], [[ENTRY]] ], [ [[P]], [[VECTOR_SCEVCHECK]] ], [ [[P]], [[VECTOR_MEMCHECK]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL4:%.*]] = phi ptr [ [[IND_END3]], [[MIDDLE_BLOCK]] ], [ [[P2]], [[ENTRY]] ], [ [[P2]], [[VECTOR_SCEVCHECK]] ], [ [[P2]], [[VECTOR_MEMCHECK]] ]
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[I:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[NEXTI:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[PTR:%.*]] = phi ptr [ [[P:%.*]], [[ENTRY]] ], [ [[PTR_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[PTR2:%.*]] = phi ptr [ [[P2:%.*]], [[ENTRY]] ], [ [[PTR2_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[NEXTI:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[PTR:%.*]] = phi ptr [ [[BC_RESUME_VAL2]], [[SCALAR_PH]] ], [ [[PTR_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[PTR2:%.*]] = phi ptr [ [[BC_RESUME_VAL4]], [[SCALAR_PH]] ], [ [[PTR2_NEXT:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    [[X0:%.*]] = load i32, ptr [[PTR]], align 4
 ; CHECK-NEXT:    [[Y0:%.*]] = add i32 [[X0]], 1
 ; CHECK-NEXT:    store i32 [[Y0]], ptr [[PTR2]], align 4
-; CHECK-NEXT:    [[PTR_NEXT]] = getelementptr inbounds i8, ptr [[PTR]], i64 [[STRIDE:%.*]]
+; CHECK-NEXT:    [[PTR_NEXT]] = getelementptr inbounds i8, ptr [[PTR]], i64 [[STRIDE]]
 ; CHECK-NEXT:    [[PTR2_NEXT]] = getelementptr inbounds i8, ptr [[PTR2]], i64 [[STRIDE]]
 ; CHECK-NEXT:    [[NEXTI]] = add i64 [[I]], 1
 ; CHECK-NEXT:    [[DONE:%.*]] = icmp eq i64 [[NEXTI]], 1024
-; CHECK-NEXT:    br i1 [[DONE]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK-NEXT:    br i1 [[DONE]], label [[EXIT]], label [[LOOP]], !llvm.loop [[LOOP22:![0-9]+]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;