[InstCombine] Remove redundant cast of GEP fold (NFC)

With opaque pointers, zero-index GEPs will be eliminated in
general.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1916,29 +1916,6 @@ Instruction *InstCombinerImpl::visitIntToPtr(IntToPtrInst &CI) {
   return nullptr;
 }
 
-/// Implement the transforms for cast of pointer (bitcast/ptrtoint)
-Instruction *InstCombinerImpl::commonPointerCastTransforms(CastInst &CI) {
-  Value *Src = CI.getOperand(0);
-
-  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
-    // If casting the result of a getelementptr instruction with no offset, turn
-    // this into a cast of the original pointer!
-    if (GEP->hasAllZeroIndices() &&
-        // If CI is an addrspacecast and GEP changes the poiner type, merging
-        // GEP into CI would undo canonicalizing addrspacecast with different
-        // pointer types, causing infinite loops.
-        (!isa<AddrSpaceCastInst>(CI) ||
-         GEP->getType() == GEP->getPointerOperandType())) {
-      // Changing the cast operand is usually not a good idea but it is safe
-      // here because the pointer operand is being replaced with another
-      // pointer operand so the opcode doesn't need to change.
-      return replaceOperand(CI, 0, GEP->getOperand(0));
-    }
-  }
-
-  return commonCastTransforms(CI);
-}
-
 Instruction *InstCombinerImpl::visitPtrToInt(PtrToIntInst &CI) {
   // If the destination integer type is not the intptr_t type for this target,
   // do a ptrtoint to intptr_t then do a trunc or zext.  This allows the cast
@@ -1980,7 +1957,7 @@ Instruction *InstCombinerImpl::visitPtrToInt(PtrToIntInst &CI) {
     return InsertElementInst::Create(Vec, NewCast, Index);
   }
 
-  return commonPointerCastTransforms(CI);
+  return commonCastTransforms(CI);
 }
 
 /// This input value (which is known to have vector type) is being zero extended
@@ -2702,11 +2679,9 @@ Instruction *InstCombinerImpl::visitBitCast(BitCastInst &CI) {
   if (Instruction *I = foldBitCastSelect(CI, Builder))
     return I;
 
-  if (SrcTy->isPointerTy())
-    return commonPointerCastTransforms(CI);
   return commonCastTransforms(CI);
 }
 
 Instruction *InstCombinerImpl::visitAddrSpaceCast(AddrSpaceCastInst &CI) {
-  return commonPointerCastTransforms(CI);
+  return commonCastTransforms(CI);
 }

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -131,7 +131,6 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   Instruction *FoldShiftByConstant(Value *Op0, Constant *Op1,
                                    BinaryOperator &I);
   Instruction *commonCastTransforms(CastInst &CI);
-  Instruction *commonPointerCastTransforms(CastInst &CI);
   Instruction *visitTrunc(TruncInst &CI);
   Instruction *visitZExt(ZExtInst &Zext);
   Instruction *visitSExt(SExtInst &Sext);