I64lowering: fix BigInt mixing with Number values

When compiling with the -O0 flag, the CheerpWriter would use
BigInt for the indices of get element ptr instructions that were never
lowered to 32-bit integers. Therefore it is good to implement the lowering
of 64-bit indices of GEP in the I64lowering pass so node does not complain
when executing the js file.

Author: Andres Madrid Ucha

llvm/lib/CheerpUtils/I64Lowering.cpp

@@ -914,7 +914,40 @@ struct I64LoweringVisitor: public InstVisitor<I64LoweringVisitor, HighInt>
 	{
 		return visitDivRem(I, "__udivti3");
 	}
+	HighInt visitGetElementPtrInst(GetElementPtrInst& I)
+	{
+		bool hasI64Index = false;
+		for (Value *Index : I.indices())
+		{
+			if (Index->getType()->isIntegerTy(64))
+			{
+				hasI64Index = true;
+				break;
+			}
+		}
+		if (!hasI64Index)
+			return HighInt();
+		IRBuilder<> Builder(&I);
+		SmallVector<Value*, 8> NewIndices;
+		for (Value *Index : I.indices())
+		{
+			if (Index->getType()->isIntegerTy(64))
+			{
+				HighInt H = visitValue(Index);
+				NewIndices.push_back(H.low);
+			}
+			else
+				NewIndices.push_back(Index);
+		}
+        Value* NewGEP = Builder.CreateGEP(I.getSourceElementType(), I.getPointerOperand(), NewIndices, I.getName());
+        cast<GetElementPtrInst>(NewGEP)->setIsInBounds(I.isInBounds());
+
+        I.replaceAllUsesWith(NewGEP);
+        ToDelete.push_back(&I);
+        Changed = true;
 
+        return HighInt();
+	}
 	HighInt visitFreeze (Instruction &I)
 	{
 		if(!I.getType()->isIntegerTy(64))