[InstCombine] Restore splat gep support in OptimizePointerDifference()

When looking for the common base pointer, support the case where
the type changes because the GEP goes from pointer to vector of
pointers. This was supported prior to #142958.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2088,8 +2088,6 @@ CommonPointerBase CommonPointerBase::compute(Value *LHS, Value *RHS) {
   // Find common base and collect RHS GEPs.
   while (true) {
     if (Ptrs.contains(RHS)) {
-      if (LHS->getType() != RHS->getType())
-        return Base;
       Base.Ptr = RHS;
       break;
     }
@@ -2132,12 +2130,15 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
   // TODO: We should probably do this even if there is only one GEP.
   bool RewriteGEPs = !Base.LHSGEPs.empty() && !Base.RHSGEPs.empty();
 
-  Type *IdxTy = DL.getIndexType(Base.Ptr->getType());
+  Type *IdxTy = DL.getIndexType(LHS->getType());
   auto EmitOffsetFromBase = [&](ArrayRef<GEPOperator *> GEPs,
                                 GEPNoWrapFlags NW) -> Value * {
     Value *Sum = nullptr;
     for (GEPOperator *GEP : reverse(GEPs)) {
       Value *Offset = EmitGEPOffset(GEP, RewriteGEPs);
+      if (Offset->getType() != IdxTy)
+        Offset = Builder.CreateVectorSplat(
+            cast<VectorType>(IdxTy)->getElementCount(), Offset);
       if (Sum)
         Sum = Builder.CreateAdd(Sum, Offset, "", NW.hasNoUnsignedWrap(),
                                 NW.isInBounds());

llvm/test/Transforms/InstCombine/sub-gep.ll

@@ -998,11 +998,7 @@ define i64 @multiple_geps_inbounds_nuw(ptr %base, i64 %idx, i64 %idx2) {
 
 define <2 x i64> @splat_geps(ptr %base, <2 x i64> %idx1, <2 x i64> %idx2) {
 ; CHECK-LABEL: @splat_geps(
-; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr inbounds i8, ptr [[BASE:%.*]], <2 x i64> [[IDX1:%.*]]
-; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr inbounds i8, ptr [[BASE]], <2 x i64> [[IDX2:%.*]]
-; CHECK-NEXT:    [[GEP1_INT:%.*]] = ptrtoint <2 x ptr> [[GEP1]] to <2 x i64>
-; CHECK-NEXT:    [[GEP2_INT:%.*]] = ptrtoint <2 x ptr> [[GEP2]] to <2 x i64>
-; CHECK-NEXT:    [[D:%.*]] = sub <2 x i64> [[GEP2_INT]], [[GEP1_INT]]
+; CHECK-NEXT:    [[D:%.*]] = sub nsw <2 x i64> [[IDX2:%.*]], [[IDX1:%.*]]
 ; CHECK-NEXT:    ret <2 x i64> [[D]]
 ;
   %gep1 = getelementptr inbounds i8, ptr %base, <2 x i64> %idx1
@@ -1015,12 +1011,10 @@ define <2 x i64> @splat_geps(ptr %base, <2 x i64> %idx1, <2 x i64> %idx2) {
 
 define <2 x i64> @splat_geps_multiple(ptr %base, i64 %idx0, <2 x i64> %idx1, <2 x i64> %idx2) {
 ; CHECK-LABEL: @splat_geps_multiple(
-; CHECK-NEXT:    [[GEP0:%.*]] = getelementptr inbounds i8, ptr [[BASE:%.*]], i64 [[IDX0:%.*]]
-; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr inbounds i8, ptr [[GEP0]], <2 x i64> [[IDX1:%.*]]
-; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr inbounds i8, ptr [[BASE]], <2 x i64> [[IDX2:%.*]]
-; CHECK-NEXT:    [[GEP1_INT:%.*]] = ptrtoint <2 x ptr> [[GEP1]] to <2 x i64>
-; CHECK-NEXT:    [[GEP2_INT:%.*]] = ptrtoint <2 x ptr> [[GEP2]] to <2 x i64>
-; CHECK-NEXT:    [[D:%.*]] = sub <2 x i64> [[GEP2_INT]], [[GEP1_INT]]
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <2 x i64> poison, i64 [[IDX0:%.*]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <2 x i64> [[DOTSPLATINSERT]], <2 x i64> poison, <2 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw <2 x i64> [[DOTSPLAT]], [[IDX1:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = sub nsw <2 x i64> [[IDX2:%.*]], [[TMP1]]
 ; CHECK-NEXT:    ret <2 x i64> [[D]]
 ;
   %gep0 = getelementptr inbounds i8, ptr %base, i64 %idx0