Analysis: gep inbounds (gep inbounds (...)) is inbounds.

[efriedma]

LGTM.

llvm/lib/Analysis/ConstantFolding.cpp

Constant* StripPtrCastKeepAS(Constant* Ptr, Type *&ElemTy) {
   return Ptr;
 }
 
 /// If we can symbolically evaluate the GEP constant expression, do so.
 Constant *SymbolicallyEvaluateGEP(const GEPOperator *GEP,
                                   ArrayRef<Constant *> Ops,
                                   const DataLayout &DL,
                                   const TargetLibraryInfo *TLI) {
+  bool InBounds = GEP->isInBounds();
   Type *SrcElemTy = GEP->getSourceElementType();
   Type *ResElemTy = GEP->getResultElementType();
   Type *ResTy = GEP->getType();
   if (!SrcElemTy->isSized())
     return nullptr;
 
   if (Constant *C = CastGEPIndices(SrcElemTy, Ops, ResTy, DL, TLI))
     return C;
APInt Offset =
       APInt(BitWidth,
             DL.getIndexedOffsetInType(
                 SrcElemTy,
                 makeArrayRef((Value * const *)Ops.data() + 1, Ops.size() - 1)));
   Ptr = StripPtrCastKeepAS(Ptr, SrcElemTy);
 
   // If this is a GEP of a GEP, fold it all into a single GEP.
   while (auto *GEP = dyn_cast<GEPOperator>(Ptr)) {
+    InBounds &= GEP->isInBounds();
+
     SmallVector<Value *, 4> NestedOps(GEP->op_begin() + 1, GEP->op_end());
 
     // Do not try the incorporate the sub-GEP if some index is not a number.
     bool AllConstantInt = true;
     for (Value *NestedOp : NestedOps)
       if (!isa<ConstantInt>(NestedOp)) {
         AllConstantInt = false;
         break;
Constant *SymbolicallyEvaluateGEP(const GEPOperator *GEP,
 
   // If we haven't used up the entire offset by descending the static
   // type, then the offset is pointing into the middle of an indivisible
   // member, so we can't simplify it.
   if (Offset != 0)
     return nullptr;
 
   // Create a GEP.
-  Constant *C = ConstantExpr::getGetElementPtr(SrcElemTy, Ptr, NewIdxs);
+  Constant *C =
+      ConstantExpr::getGetElementPtr(SrcElemTy, Ptr, NewIdxs, InBounds);
   assert(C->getType()->getPointerElementType() == Ty &&
          "Computed GetElementPtr has unexpected type!");
 
   // If we ended up indexing a member with a type that doesn't match
   // the type of what the original indices indexed, add a cast.
   if (Ty != ResElemTy)
     C = FoldBitCast(C, ResTy, DL);
 

llvm/test/Other/constant-fold-gep.ll

 @M = constant i64* getelementptr (i64, i64* null, i32 1)
 @N = constant i64* getelementptr ({ i64, i64 }, { i64, i64 }* null, i32 0, i32 1)
 @O = constant i64* getelementptr ([2 x i64], [2 x i64]* null, i32 0, i32 1)
 
 ; Fold GEP of a GEP. Very simple cases are folded without targetdata.
 
 ; PLAIN: @Y = global [3 x { i32, i32 }]* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 2)
 ; PLAIN: @Z = global i32* getelementptr inbounds (i32, i32* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 0, i64 1, i32 0), i64 1)
-; OPT: @Y = local_unnamed_addr global [3 x { i32, i32 }]* getelementptr ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 2)
+; OPT: @Y = local_unnamed_addr global [3 x { i32, i32 }]* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 2)
 ; OPT: @Z = local_unnamed_addr global i32* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 0, i64 1, i32 1)
-; TO: @Y = local_unnamed_addr global [3 x { i32, i32 }]* getelementptr ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 2)
+; TO: @Y = local_unnamed_addr global [3 x { i32, i32 }]* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 2)
 ; TO: @Z = local_unnamed_addr global i32* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 0, i64 1, i32 1)
 
 @ext = external global [3 x { i32, i32 }]
 @Y = global [3 x { i32, i32 }]* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 1), i64 1)
 @Z = global i32* getelementptr inbounds (i32, i32* getelementptr inbounds ([3 x { i32, i32 }], [3 x { i32, i32 }]* @ext, i64 0, i64 1, i32 0), i64 1)
 
 ; Duplicate all of the above as function return values rather than
 ; global initializers.